OK

daijr/s

I don't think 短い's sense 2 is an antonym. In daijr, "short (time)" and "brief" are separate senses (with "短い小説" given as an example of the latter). Sense 1 on our 短い covers both spatial and temporal usage.
In daijr/s, sense 1 is restricted to 長い.

@@ -19,0 +20 @@
+<stagk>長い</stagk>
@@ -26 +26,0 @@
-<xref type="ant" seq="1418620">短い・2</xref>

GG5: long; lengthy; 〔長引いた〕 prolonged; protracted
中辞典: (1) 〈空間的に〉 long (2) 〈時間的に〉 long; lengthy (長ったらしい)
ルミナス: (1) 《長さ･距離》: long (←→short) (2) [adj] long (←→short); (長たらしい) lengthy. [adv] (長く･長い間) long.
Daijr/s - both have 3 senses - time/distance/durability

I still prefer to have more glosses, partly because this data is being used in a reverse direction, so a reasonable spread of terms is appropriate. The meanings do fairly cleanly break into two groupings - spatial and temporal and the fact that English uses the same term for both doesn't stop it being two senses.

@@ -23 +23 @@
-<gloss>long (distance)</gloss>
+<gloss>long (distance, length)</gloss>
@@ -26,0 +27,2 @@
+<xref type="ant" seq="1418620">短い・2</xref>
+<xref type="ant" seq="1418620">短い・2</xref>
@@ -28 +29,0 @@
-<gloss>lengthy</gloss>
@@ -29,0 +31 @@
+<gloss>prolonged</gloss>

The anonymous contributor is correct. I think that it would be totally reasonable to gloss this simply as “long” and nothing else, because 長い can be used 
with anything. The way this is written may be misleading to users who might think that they can’t use it to say “long hair”, for example.
“lengthy” and “protracted” don’t quite fit. “lengthy” gives a sense of extensive length. Wisdom translates it as 長く続く; 長すぎる. Even though it’s entry 
also has “lengthy” as a gloss, it’s only used to make the English example sentences sound a bit more natural. I don’t think it’s necessary and I think it’s 
better to direct users to a word that can a connotation of “too long” in Japanese.
“protracted” means prolonged or extended, and Wisdom translates it as 長引く, 長期化した, and it isn’t mentioned in the entry for 長い.