One thing, and one that's relevant to an OS class, that I've been doing with my own toy kernel (that I haven't had any time for lately) is using Cargo workspaces to make it extremely modular. You can of course do this in C, but it's even easier with Cargo. In a class context, you could do something like "here's the entire OS except the scheduler package, implement it and make all the tests pass."
This is true. I wonder if we'll see an OS where each of these modules has some sort of monadic (or maybe something else) API so that you can really decouple the implementation from the API.
