Just a suggestion: the words for “the day before yesterday / after tomorrow”. I know they are pretty basic vocabulary, but they are quite common words with irregular readings of the kanji which could be a very valuable addition to WK. I always kinda forget how they are supposed to be read or written…
明後日 and 一昨日
In addition, their week/month/year counterparts could be added for the sake of completion. Some are already in WK, so I can’t see a reason why not to add the others.
再来週 and 先々週 (only the first one is in WK)
再来月 and 先々月 (both already in WK)
再来年 and 一昨年 (none in WK)
I’ve found this one https://www.wanikani.com/kanji/岐 = Branch off, but default vocabularies are only place names, 岐阜 and 岐阜県, which also use a non-standard (表外) reading (ぎ).
Perhaps some vocabularies to suggest would be 多岐, 分岐点, 岐路.