Minor suggestion: currently, SM-2 retention is capped between 0.7 and 0.97, just like desired retention. However, SM-2 retention could very well be outside of those bounds for some users. I don’t think there is a good reason to cap it the same way as desired retention.
And one more thing I’m worried about: new users who haven’t heard about FSRS before won’t know what “difficulty”, “stability,” and “retrievability” mean. But I don’t know how to solve this problem. In this issue I suggested including a pre-made deck about Anki itself, so users can use Anki to learn about Anki, but it seems like that’s not planned. Updating the manual to include new terms would be nice, but not every user reads the Anki manual, in fact, I’m pretty sure the majority of users don’t. So I don’t know how to make sure that new users aren’t confused.