Python is considerably more dynamic than JavaScript. And I'm not trying to drag pypy, just saying that that's already the state of the art and there are good reasons that the authors of pypy didn't set out to do what Mojo apparently claims to have done.
> Python is considerably more dynamic than JavaScript
This is sometimes repeated but I don’t believe that is why Python is slow (nor do I think for most measures of “dynamic” it is even true). Which aspect of “dynamism” in particular are you concerned about that JavaScript lacks? The primary hindrance is keeping CPython extensions working while making Python fast. Add to that the hundreds of millions that went into V8 and other JavaScript implementation efforts.
For starters, consider that almost every operator in Python is a dynamic method call under the hood. This includes value equality and hashing, which also affects e.g. dict keys. Oh, and all built-in types can be extended and their behavior overridden.
Those are hardly unsolvable issues with a JIT as they are static for the vast majority of cases. Solutions have been proposed since the 90s with Self and Strongtalk[1].
Doing that, plus 100% compatibility with CPython extension API, while preserving some expectations of deterministic destruction in Python, are the challenges one would face.
