Me too, but changing the referential semantics would be a massive breaking change. That doesn't qualify as "without changing much of a codebade". And tacking on a giant new orthogonal type system to avoid breaking existing code would be akin to creating a new language. Why bother when you can just write Python modules in Rust.

I’d like to be good looking and drive a Ferrari. But that probably isn’t going to happen, either.

Any program written in Python of any significant size is literally a soup of multiple languages.