I've read that it can't even be as fast as JS, because everything is monkey-patchable at runtime. Maybe they can optimize for that when it doesn't happen, but remains to be seen.
Python is probably much more monkey patchable. Almost any monkey patching that JavaScript supports also works in Python (e.g. modifying class prototype = assigning class methods), but there are a few things that only Python can do: accessing local variables as dict, access other stack frames, modifying function bytecode, read/write closure variables, patching builtins can change how the language works (__import__, __build_class__). Many of them can make a language hard to optimize.
You can always use optimistic optimization strategies where you profile the fast path and optimize that. When someone does something slow, you tell them to stop doing it if they want better performance.
In any case, that should be irrelevant to getting a reasonably performant JIT running. Lots of AOT and JIT compiled languages have robust FFI functionality.
The native extensions are more relevant when we talk about removing the GIL, since lots of Python code may call into non thread safe C extension code.
It is a non-optimizing bytecode interpreter and it makes no use of JIT compilation.
JavaScript with V8 or any other modern JIT JS engine runs circles around it.
Go, Java, and C# are an order of magnitude faster but they have type systems that make optimizing compilation much easier.
There's no language-inherent reason why Python can't be at least as fast as JavaScript.