OK

@@ -6,4 +5,0 @@
-</k_ele>
-<k_ele>
-<keb>性質</keb>
-<ke_inf>&sK;</ke_inf>

https://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q112424686
> 「性質悪い」と書いて、「タチわるい」と読めますか？
> …「性質（たち）」は、昔使われていた熟字訓です。一般に使う人がいるかどうかは分かりませんが、小説ではよく使われますね。

Google N-gram Corpus Counts
╭─ーーーーー─┬─────────┬───────╮
│ タチが悪い │  69,714 │ 25.5% │
│ たちが悪い │  63,549 │ 23.3% │
│ 質が悪い　 │ 110,991 │ 40.6% │
│ 性質が悪い │  29,014 │ 10.6% │
╰─ーーーーー─┴─────────┴───────╯

「性質(たち)が悪い」 is pretty common in written media. I've seen it before and I bet this edit originally came to us because the anonymous contributor came across it.

I'm not a fan of using the [sK] tag for jukujikun/gikun forms. It's not one of the types mentioned in the editorial policy.
I think it would be better to drop 性質 here entirely and add a 「性質が悪い」 form to the entry 2259540　(タチが悪い) instead. I think that might be enough to handle it.

[uk] seems fine to me. The referenced chiebukuro post also says 『相手に「たち」と伝えたければ、仮名書きが一般的です。』

In 1375390: Stephen wrote: "Sankoku 8e added 性質 as a jukujikun form for たち【質】. I don't see it in other refs."
GG5, etc. use kana for all examples of たち. and our 3 example sentences use kana too.

Proposing [uk]. Moving the 性質/たち suggestion from 1375390. We could have a note saying たち is a gikun reading of 性質, but I'd be happy just to add it as a search-only form.

@@ -5,0 +6,4 @@
+</k_ele>
+<k_ele>
+<keb>性質</keb>
+<ke_inf>&sK;</ke_inf>
@@ -11,0 +16 @@
+<misc>&uk;</misc>
@@ -17,0 +23 @@
+<misc>&uk;</misc>

gg5, prog, daij

Not just people.

@@ -12 +12 @@
-<gloss>nature (of person)</gloss>
+<gloss>nature (of a person)</gloss>
@@ -15 +15,7 @@
-<gloss>quality</gloss>
+</sense>
+<sense>
+<pos>&n;</pos>
+<gloss>nature (of something)</gloss>
+<gloss>character</gloss>
+<gloss>kind</gloss>
+<gloss>sort</gloss>

GG5, etc.

Making it clearer how 質/たち and 質/しつ differ.

@@ -11,0 +12,3 @@
+<gloss>nature (of person)</gloss>
+<gloss>disposition</gloss>
+<gloss>temperament</gloss>
@@ -13 +15,0 @@
-<gloss>nature (of person)</gloss>