I'm super happy to see this project. I was thinking about doing something similar a while ago to use in flashcards. I find spaced repetition really useful in a lot of areas, but for math exercises it never really made sense as I would just memorize the answer rather than actually doing the calculation to see if I remember the steps! Ultimately I gave up as it felt like a way to procrastinate by doing something I like (programming) instead of something I don't really enjoy (math).

I might poke around with this and Anki sometime though and see if I was onto something!