Interesting ideas for how to write the cards. But the dependency part seems to be limited to letting you pick questions from a subtree. SuperMemo has something similar, which is the closest I was able to find in existing solutions.

The problem is that this basically means dependencies can only form a tree, with one topic depending on only in at most one other topic. What I wanted was something that let me express the relationships as a directed acyclic graph. Something like learning a big chunk of a music piece is dependent on the questions for learning individual smaller passages. Something as basic as that cannot really be expressed with a tree but is trivial with a DAG.