Wow, this is nice!
But, as far as I can see, it only uses the public C-API and does not need any changes in CPython itself.
Your next step would be to release it as a C library – even if you do want to integrate this into CPython, it’ll be easiest if it exists in an immediately usable form (and even after it’s accepted, as a “backport” for existing Python versions).
Similarly: instead of a PEP, write documentation. You can turn docs into a PEP if you want to go that way.
If you go that way, please choose a different prefix for the API names; keep Py* for the PEP.
To set expectations: I don’t think this needs to be in CPython itself. I know that sounds disappointing, but after all, Python is made to be extendable; we want to have interesting projects outside the core.