Idea for the Japanese Course
To help with Kanji learning, why don't you add a little toggle at the top of the lesson with 5 settings, no kanji, little kanji, moderate kanji, many kanji, and Fluent Kanji. This way, once people are fine with reading it in Kana, they can gradually increase the amount of Kanji they learn.
Or you could split the tree into NLPT sections. Like the first 3-4 groupings are NLPT 5, then the next 3-4 are NLPT 4. And as you progress through the NLPT levels, more kanji in earlier levels are unlocked for you to learn.
Or a mixture of both.
I think it's unfortunately too late to incorporate a feature like this, but I really hope that they add more Kanji one way or another in the future. One of the things I was really hoping for was learning more Kanji, but unfortunately I already knew most of the ones in the course.
TBH, I never really understood the grouping of Kanji based on JLPT level. It would make much more sense if the N5 Kanji were the Kanji that make up the N5 words rather than ~80 pretty basic Kanji.
I love the idea of a toggle for Kanji.
I even think a single setting (full Kanji vs. status quo) would be a huge improvement. For example, if I were designing a course, I'd probably make the "full Kanji" setting not show ALL Kanji but show all Kanji that are in common / widespread use, i.e. omitting it only for words that are typically written in hiragana or words for which the Kanji is not widely used.
If they had little hiragana spellings above or below the Kanji (like many textbooks do) or had the hiragana in the hover-over hints, I think most people would probably opt to learn the Kanji, but the people who rely on the hiragana or forget how a word is pronounced could still see it...it's like a best of both worlds.