I think one could radically change the way Python objects work internally, and have the C foreign function interface (FFI) wrap every object passed to a C extension in an API/ABI-preserving facade

HPy is building an API abstraction layer which is designed to be used with both the CPython API and JITs. However, IIUC they are not proposing any changes to CPython itself, but rather to provide a smaller API surface and fewer JIT impedance mismatches when extensions are built against something other than CPython. The lead developer is a longtime PyPy developer.

https://hpyproject.org/ (https://github.com/hpyproject/hpy)