Amazing work! In https://rember.com the main unit is a note representing a concept or idea, plus some flashcards associated to it, hsrs would fit perfectly! I'll look more deeply into it.
however, individual grammar outputs aren't their own cards, you get a fresh example every time you see a card. this requires a very different scheduling approach, since you have to estimate how all the cards in the 'call tree' contribute to the overall result and reschedule them as well https://github.com/satchelspencer/hsrs/blob/main/docs/overvi...