That's a really intriguing idea! Though even equipped with a tool like this, I think it would be difficult to use SRS for learning math or computer science concepts. The process might look something like:

1. learn the concept

2. break it into atomic question/answer pairs

3. define some dependence relation for all these pairs (X is foundational to Y and Z but not A)

4. input them into your SRS of choice

Each of these steps require significant amounts of time and brainpower. Also it would be harder if you were still learning the concept since you'd continually need to go back and redefine relations as your understanding grew.

On the one hand all this would be a great way to understand a subject. On the other, one could argue that it's very inefficient, and it would be better to not bring SRS into it all all. Compare this to say a vocabulary card, which you make, enter into SRS, then you're done. So far this (the vocab thing I mean) is the only SRS use-case that makes sense for me.

Thing is, many people use SRS to keep things memorized that they don't want to forget about. For this use case, you don't need to care much about dependencies and the like, so making your own deck should be quite simple. The "learn/figure out new stuff" case is somewhat different, and plenty of people use pre-made decks with advanced features e.g. to learn vocab, or some sort of basic knowledge in some other subject.

Another possibility might be to show X, and then if the user fails, work back through the dependencies.

The hard part might be the UI for finding and selecting the dependencies for a new item.