I don't think we can be sure that the mugwort sense is rare. Wikipedia mentions it.

@@ -17,2 +17 @@
-<xref type="see" seq="1517830">蓬・1</xref>
-<misc>&rare;</misc>
+<xref type="see" seq="1517830">ヨモギ・1</xref>

艾
https://furigana.info/w/艾
もぐさ	68.4%
よもぎ	26.3%
ガイ	5.3%

Moxibustion:
https://ja.wikipedia.org/wiki/灸
灸（きゅう、やいと）とは、艾（もぐさ＝ヨモギの葉の産毛を陰干し・精製取得したもの）...

https://en.wikipedia.org/wiki/Moxibustion
Moxibustion (Chinese: 灸; pinyin: jiǔ) is a traditional Chinese medicine therapy which consists of burning dried mugwort (wikt:moxa) on particular points on the body.

https://kotobank.jp/word/艾-645287
も‐ぐさ【×艾】
《燃え草の意》<---- means burnable grass
１ ヨモギの葉を干し、臼でついて作る綿状のもの。灸きゅうを据える際に燃やす材料。焼き草。
２ ヨモギの別名。

The whole process of making mogusa from yomogi (from growing the plant, to drying and processing it)
もぐさを作ってみよう
http://www.rakko-do.com/terakoya04.html

https://en.wikipedia.org/wiki/Moxa
Moxa may refer to:
Moxa, material used in moxibustion, a Chinese traditional medicine
Mihail Moxa (1550–1650), Romanian historiographer and translator
Moxa, Thuringia, Germany, municipality
Moxa Technologies, Taiwanese company

Sankoku does not have [2]. 

Japanese Wikipedia moxibustion(灸) opening line explains the relationship between ヨモギ and もぐさ(ref).

I gifted a bottle of Jeppson's Malört, a bitter herbal liquor, to a Japanese friend, who in turn introduced me to the term 蓬 ヨモギ(mugwart), which has 艾 listed as a secondary kanji form.  I can only speculate, but I have to imagine that 艾 when read as  もぐさ (literally "burnable/burning grass", pointed out by daijs) in modern Japanese is generally going to mean [1]. 

We might not generally write in an explanation for "moxa", but without one the very-relevant xref (moxa => moxibustion) will be very confusing.  Also, "moxa" does not readily produce an explanation on google.  And, a little info in [1] explains the relationship between [1] and [2] nicely.  

I doubt many people know what moxa is (let alone moxibustion), so a little info may not hurt, at least for disambiguation.

If [2] didn't already xref 蓬[1], I would say that [1] should.

@@ -12 +12,2 @@
-<gloss>moxa</gloss>
+<xref type="see" seq="2064140">灸</xref>
+<gloss>moxa (dried mugwort leaf used in moxibustion)</gloss>
@@ -16,0 +18 @@
+<misc>&rare;</misc>

@@ -16,2 +16,2 @@
-<xref type="see" seq="1517830">蓬</xref>
-<gloss>Japanese mugwort</gloss>
+<xref type="see" seq="1517830">蓬・1</xref>
+<gloss>Japanese mugwort (Artemisia princeps)</gloss>

Entry created