詩を歌う	2334
詩を詠う	1152

詩を歌って	1851
詩を詠って	278


詩を歌わ	330
詩を詠わ	46

Maaaybe here, though? But it's still a bit of a stretch, all of these added together. The point of the rK as I see it isn't to say 
"this kanji might as well not have been included in this entry at all, it's completely pointless" but to tell esp. early learners 
that it's quite rare and that they don't need to bother learning it by heart to feel they "know" the word in question, and also to 
provide guidance for reverse lookups. It's not to say they won't ever, in a lifetime of reading Japanese, possibly come across it or 
find reason to use it. Since we do mention it in a note on sense 2, and considering these ngrams, I'm OK with removing it, though.

@@ -15 +14,0 @@
-<ke_inf>&rK;</ke_inf>

心を詠った	174
心を歌った	2030
心を唄った	140
心を謳った	54
故郷を詠った	32
故郷を歌った	277
故郷を唄った	No matches
故郷を謳った	No matches
愛を唄った	590
愛を謳った	674
愛を歌った	4023
愛を詠った	137

the daijs example is 故郷の心を-った. daijr is 愛
の美しさ-った

I don't think this shows it rising above being 
a rK.

I think the application of rK has to be 
percentage-based, nothing else makes sense or 
is actually helpful. If it's a lot more common 
for a particular sense than overall, I 
wouldn't tag it as rK though. But how common 
is it for sense 2?

gg5, prog, dajij
美しさを歌った	274
美しさを詠った	51

Do we really want to tag a form with 34k in the ngrams as "rare"? I know it's less than 1% of 歌う's count but the difference is probably a lot 
smaller if you look only at sense 2 usage (詠う doesn't apply to sense 1).

@@ -43,3 +43,3 @@
-<gloss>to sing (one's praises in a poem, etc.)</gloss>
-<gloss>to compose a poem</gloss>
-<gloss>to recite a poem</gloss>
+<gloss>to sing of (love, beauty, etc.) in a poem</gloss>
+<gloss>to express in the form of a poem</gloss>
+<gloss>to recite (a poem)</gloss>

歌う	4222623
唄う	351406
詠う	34216
謡う	14340
唱う	14235

I don't think 唄う is spec1 worthy

@@ -12 +12,4 @@
-<ke_pri>spec1</ke_pri>
+</k_ele>
+<k_ele>
+<keb>詠う</keb>
+<ke_inf>&rK;</ke_inf>
@@ -16,4 +19 @@
-<ke_pri>ichi2</ke_pri>
-</k_ele>
-<k_ele>
-<keb>詠う</keb>
+<ke_inf>&rK;</ke_inf>
@@ -22,0 +23 @@
+<ke_inf>&rK;</ke_inf>