See below.

I came. I saw. I failed.

でも、いったいなに、おもしろいでしたよ。

[I hope that is right!]

I think the entry is already quite clear.  I don't see why this entry should be 
singled out for addition of romaji, and I really don't see how adding romaji would 
help in any case.

See below.

I appreciate your taking all this trouble over my submission. It is just a pity that the system does not allow you to include Japanese in the glosses.

Just one final thought before you close the discussion down. I know that you do not like using romaji, but would it be intolerable to include it in this case, for example: (e.g. "why in the world? (ittainaze)"), etc.

What you are raising is the issue of having examples of the use of 一体. That 一体なぜ is one such, rather than it being a formal dictionary entry. It's the same in GG5, etc.
In JMdict we are sticking with the appropriate (I think) choice of what actually are headwords, and having examples, such as 一体なぜ, separate. If you look up 一体 in WWWJDIC you'll see the example "一体どこで彼に会ったんだ。 Where on earth did you meet him?". Normally we try and have one example per sense, but I have just flagged "いったいなぜ彼を駅に連れて行ったの？" as well (it will appear in a week, as Tatoeba's downloads are prepared weekly.)

See below.

Thank you for giving the time to explain your stand on this matter. I appreciate that because I am the novice here and I am keen to understand the complexities of the Japanese language. As I slowly work my way through Japanese text, looking for starting points and ending points of the sentence structure, I am motivated to search your site for help. When my initial search criteria does not give me any assistance, I try all sorts of other searches and sometimes I find the answer. In that way, when I have found the answer, I make a submission because I think that it may help another novice on the same route.

As to this submission, it is true that many examples of the Japanese “string of text symbols” can be found in the example sentences in the Tanaka corpus and that is, of course, some help, but they do not necessarily help with the definitive meaning of the particular “string of text symbols”, nor do they specifically help one to discover where a “headword” will start or stop so that individual entries can be analysed. In short, as between Japanese and English it often goes from idiom to idiom.

I think that it is the word “dictionary” in the context of a language like Japanese which is the hub of the problem. In English, expressions like “what on earth”, are no problem because there are three individual words in a string. Each of these words can be looked up. If I look them up in turn, in any order, e.g., "earth" first, I get the individual meanings, but I accept that I do not get a headword in the dictionary which is “what on earth”. However, [popping in to the library on my roaming] if I look up the word “earth” and read what it states, then – for example in Collins English Dictionary – I find one meaning as this: used as an intensifier in such phrases as “what on earth”, “who on earth”, etc.. Now, that matches what is in your site, except that I cannot look up the individual words for “what on earth”, etc., in Japanese; unless I already know them.

In the Japanese dictionary,“shogakukan”, it carries a link between the headwords “いったいぜんたい” and “いったい”. Likewise on your site, namely:-

一体全体; いったい全体 【いったいぜんたい】 (adv) (emph. form of 一体) ... the heck (e.g. "what the heck?"); ... in the world (e.g. "why in the world?"); ... on earth (e.g. "who on earth?")

However, in shogakukan it gives more. Under the headword “いったい” it gives “一体なぜ....” with the meaning “Why on earth ….”. Thus, like the English dictionary, with that clue, I can look up “なぜ” and see what it means. Also, under the headword “いったいぜんたい” it gives “一体全体どうした....” with a meaning of “What on earth....”, again, if necessary, I can look up “どうした” for its meaning.

My only point is this: that you have taken one helpful step on the road, namely: as in the English dictionary as noted above, by giving English meanings associated with the headword. However, I will not say, “What on earth stops you from including the “いったいなに”, “いったいなせ”, etc.” because I can imagine that a line has to be drawn somewhere; and, of course, you have also explained the mechanics of the system which prevent a simple inclusion under the main “headword”. However, the inclusion of the other expressions individually, which have already been included in English by description, would make it clear to the novice. In addition, it would even make clearer the usage in the helpful sentences in the Tanaka corpus.

I really have to agree with Rene. I think this has been pushed as far as it can go.

I still don't understand why things like いったいなに need to be added.  It's 
just standard use of an adverb.  I would never expect "why on earth" to appear 
in an English-English dictionary, nor いったいなに in a Japanese-Japanese 
dictionary, so why add it to this Japanese-English dictionary itself?  There are 
plenty of example sentences in the Tanaka corpus that give this exact 
example.  I'm not even convinced that 「いったいなに」 gets the parsing of the 
sentence correct in something like 「君は一体何を言おうとしているのか。」I'd 
guess that 一体 applies to 何を言おうとしているのか, not just to 何.

See below.

Thank you for posing that as a question.

To have an expert state the obvious is the basic dream of the novice who does not understand. Unfortunately, the novice usually gets the so called “obvious” from the non-expert; in short, most of the ordinary people who actually speak the language in question. In my own tongue [English], would I believe the general speaker of my tongue when I am told the meaning of some expression? Fortunately, when the language is used in a general context, understanding is easier for the native speaker. However, when the language is used in a specific context of some importance, we often have the great brains of the courtrooms arguing over the meaning.

I have come to regard your site as the living proof of the benefit of having your experts holding discussion over the meaning and understanding of the Japanese language. Moreover, you are not tied to the long delays of the printed published word, e.g., like the OED with 20 odd volumes. When I last exchanged a note with the editors on the meaning of the word “adversarial” and its first usage, they said that my comment was timely because they were just about to start again at “A” and again work their way through to “Z”. The cycle takes years to complete. However, as I understand it, I am sure that they revel in stating the obvious, so much so, that the big OED is, in my view, the dictionary where every beginner should start; unfortunately, the shear size is is the frightener for the novice. 

With your site, sized impedes no one because the overall size is not so obvious to anyone, save those who have created it. So, for my part, to the extent which time and facilities allow you to state the obvious, every novice who searches will applaud your work with equal measure.

Those verb conjugations are machine-generated, and only appear in WWWJDIC. 
Yes, I could put things like:
一体何;一体なに [いったいなに] /(exp) (See 一体)/
but isn't it just stating the obvious? There are a heap of Japanese words (全然, 全部, 本当, etc.) which do similar things.

See below.

I think that I am beginning to understand the situation a little better. Upon reading your comments, I am wondering whether you could deal with the Japanese in a similar manner as you do with various verb endings, for example: すれば seeする. Thus, we would get an entry which reads: 一体なに (いったいなに) see 一体, etc. for each of the variables. In this way, when someone searches for “一体なに”, they will find what they are looking for and then they can click on the cross-reference and find themselves reading your main explanations under “一体” and the result would be clear to most if not all.
I hope that is helpful.

The reason being that legacy programs using the old EDICT format can't cope with Japanese in glosses. That's part of the reason for the <<notes>>.
I'm going to reverse Rene's ordering. The Tanaka sentences have 133 examples for 一体/いったい and 132 of them are for the sense we are discussing. I'd have to renumber all the sense tags (can be done), but really with this sense dominating in modern Japanese, it should be first, regardless of what the 国語s say.
I'm also changing the "exemplar" example in WWWJDIC to a better one. And I'm adding an example sentence for 一体に.

@@ -16,0 +16,7 @@
+<sense>
+<pos>&adv;</pos>
+<s_inf>before an interrogative, forms an emphatic question</s_inf>
+<gloss>...the heck (e.g. "what the heck?")</gloss>
+<gloss>...in the world (e.g. "why in the world?")</gloss>
+<gloss>...on earth (e.g. "who on earth?")</gloss>
+</sense>
@@ -37,7 +44,0 @@
-<sense>
-<pos>&adv;</pos>
-<s_inf>before an interrogative, forms an emphatic question</s_inf>
-<gloss>...the heck (e.g. "what the heck?")</gloss>
-<gloss>...in the world (e.g. "why in the world?")</gloss>
-<gloss>...on earth (e.g. "who on earth?")</gloss>
-</sense>

Japanese cannot be added to glosses.

See below.

That looks good, but would it not be possible to include the Japanese reading for each "e.g" [e.g. "what the heck?" (一体なに))] so that what is clear to the expert would also be clear to the novice?

This was in response to Francis's comment:
I can see where you are coming from in your comment "I've come round to the view that just one of quite a lot of 一体 + XXX constructions" in respect of my rejected submission for "一体なせ".
In view of that, I am wondering if this main entry could have the addition of an explanation like the following:-
gives the expressions like:...the heck, …the world, ...on earth, and followed by various question words, like, なに,　なせ,　どれ, in order to give (e.g. "what the heck?"); (e.g. "why in the world?"); (e.g. "who on earth?")
Something like that may help the novice who is searching for such expressions.

some kind of note is fine with me, although i think the glosses as given are 
sufficiently obvious.  but if it's included, i think the senses should be swapped 
so that it doesn't look like the note applies to the whole word.  the new ordering 
matches the sense ordering of kokugo dictionaries and progressive waei.  
hopefully that wouldn't mess with paul's stuff too much

@@ -16,7 +16,0 @@
-<sense>
-<pos>&adv;</pos>
-<pos>&adj-no;</pos>
-<gloss>...the heck (e.g. "what the heck?")</gloss>
-<gloss>...in the world (e.g. "why in the world?")</gloss>
-<gloss>...on earth (e.g. "who on earth?")</gloss>
-</sense>
@@ -39,1 +32,1 @@
-<pos>&adv;</pos>
+<pos>&n-adv;</pos>
@@ -44,0 +37,7 @@
+<sense>
+<pos>&adv;</pos>
+<s_inf>before an interrogative, forms an emphatic question</s_inf>
+<gloss>...the heck (e.g. "what the heck?")</gloss>
+<gloss>...in the world (e.g. "why in the world?")</gloss>
+<gloss>...on earth (e.g. "who on earth?")</gloss>
+</sense>

@@ -10,0 +10,3 @@
+</k_ele>
+<k_ele>
+<keb>陰うつ</keb>

広辞苑

@@ -15,1 +15,6 @@
-<gloss>to go through</gloss>
+<gloss>to go through, pierce, penetrate</gloss>
+</sense>
+<sense>
+<pos>&v5k;</pos>
+<pos>&vt;</pos>
+<gloss>to persist, stick to</gloss>

http://dic.yahoo.co.jp/newword?ref=1&p=パネェ&index=2007000119
http://zokugo-dict.com/26ha/panee.htm
http://www.google.com/search?hl=en&hs=6by&q="パネェ"&aq=f&aqi=g4g-mr2&aql=&oq=

I'm really not sure on the part-of-speech.

https://en.wiktionary.org/wiki/shit-eating_grin
Google images comparison

@@ -19,0 +20 @@
+<misc>&col;</misc>
@@ -21,0 +23 @@
+<gloss>shit-eating grin</gloss>

@@ -11,0 +12,5 @@
+<re_restr>どや顔</re_restr>
+</r_ele>
+<r_ele>
+<reb>ドヤがお</reb>
+<re_restr>ドヤ顔</re_restr>

@@ -5,0 +6,3 @@
+</k_ele>
+<k_ele>
+<keb>ドヤ顔</keb>

@@ -12,1 +12,2 @@
-<gloss>self-satisfied look, triumphant look</gloss>
+<gloss>self-satisfied look</gloss>
+<gloss>triumphant look</gloss>

http://dictionary.goo.ne.jp/leaf/jn2/160462/m0u/どや顔/
http://www.google.com/search?hl=en&client=firefox-a&hs=KWJ&rls=org.mozilla:en-US:official&q="どや顔"&aq=f&aqi=g10&aql=&oq=

Dropping the quotes, as we did with 1577490, etc.

@@ -15 +15 @@
-<gloss>"cool"</gloss>
+<gloss>cool</gloss>

Daijirin

Plenty of WWW pages mentioning they are the same.

@@ -8,2 +8,8 @@
-<pos>&n;</pos>
-<gloss>xref かっこいい</gloss>
+<pos>&adj-na;</pos>
+<pos>&adj-no;</pos>
+<xref type="see" seq="1577490">格好いい・かっこういい</xref>
+<misc>&col;</misc>
+<gloss>attractive</gloss>
+<gloss>good-looking</gloss>
+<gloss>stylish</gloss>
+<gloss>"cool"</gloss>

http://www.paradisearmy.com/doujin/pasok_sankakukei.htm

かっけー	50176
カッケー	19450

I think informal/slangy glosses work best here.
I think this should be exp. It's not always (or even usually) prenominal.

@@ -6,0 +7,3 @@
+<r_ele>
+<reb>カッケー</reb>
+</r_ele>
@@ -8,2 +11,2 @@
-<pos>&adj-pn;</pos>
-<xref type="see" seq="1577490">格好いい・かっこいい</xref>
+<pos>&exp;</pos>
+<xref type="see" seq="1577490">かっこいい</xref>
@@ -11,3 +13,0 @@
-<gloss>attractive</gloss>
-<gloss>good-looking</gloss>
-<gloss>stylish</gloss>
@@ -14,0 +15,4 @@
+<gloss>awesome</gloss>
+<gloss>sick</gloss>
+<gloss>sweet</gloss>
+<gloss>dope</gloss>

@@ -9 +9 @@
-<xref type="see" seq="2822320">格好いい・かっこいい</xref>
+<xref type="see" seq="1577490">格好いい・かっこいい</xref>

With ~50k in the Google n-grams, it's worth having for people to look up.

It's in jitsuyo.　Of the others you mentioned, only はえー is in a dictionary on weblio (新潟県田上町方言 dic)
km
はえー	1194
かっけー	1057
たけー	862
なげー	553
ちっちぇー	222
はつまんねー	153
おっせー	66

I question whether we should have this as an entry. So many 形容詞 can be written in this slangy style. たけー, なげー, はえー、おっせー, はつまんねー、ちっちぇー, etc.

This should not be adj-na or adj-no. I'd call it a specific 終止形/連体形 conjugation of an adj-i, so maybe just exp...?

@@ -8,2 +8 @@
-<pos>&adj-na;</pos>
-<pos>&adj-no;</pos>
+<pos>&adj-pn;</pos>

Restoring lost xref.

@@ -9,0 +10 @@
+<xref type="see" seq="2822320">格好いい・かっこいい</xref>

Dropping the quotes, as we did with 1577490, etc.

@@ -15 +15 @@
-<gloss>"cool"</gloss>
+<gloss>cool</gloss>

Daijirin

Plenty of WWW pages mentioning they are the same.

@@ -8,2 +8,8 @@
-<pos>&n;</pos>
-<gloss>xref かっこいい</gloss>
+<pos>&adj-na;</pos>
+<pos>&adj-no;</pos>
+<xref type="see" seq="1577490">格好いい・かっこういい</xref>
+<misc>&col;</misc>
+<gloss>attractive</gloss>
+<gloss>good-looking</gloss>
+<gloss>stylish</gloss>
+<gloss>"cool"</gloss>

http://www.paradisearmy.com/doujin/pasok_sankakukei.htm