Probably something like https://github.com/Microsoft/pyright (or maybe https://pyre-check.org) would help us sure up a lot of the insanity that happens at our interface boundaries.

I don't think Micro/Circuit Python support PEP-526, so we'd be leaning on PEP-484 and whatever subset of pyright's features can fit PEP-484 syntax, but that's alright. Alternatively, we could check to see if there's a Python 3.10 to 3.5 transpiler out there that would strip, say, type aliases or rewrite pattern matches, at compile time (given that my day job is TypeScript, I'm innately familiar with this concept, but I don't know if it's made its way into Python-land yet. It could be an interesting project to write if it doesn't exist, though...)

Another thing worth noting is that we'd need to ensure that https://github.com/python/typeshed (or a similar collection we and/or Adafruit maintains - this might be something to chat with @tannewt about) has type stubs for CircuitPython's stdlib, which would be a fairly non-trivial undertaking. We only use a small subset of CircuitPython's API, though, so doing a partial type stub writeup probably wouldn't be nightmarish.