@elhult
Python has at least 3 JIT implementations #PyPy and #Numba, and also #Pyjion - all three take completely different approaches. I suspect this poll is more about the Pyjion approach. I think scientific computing applications would benefit more from a JIT in CPython.
Multithreading while lightweight and possibly truly parallel without a GIL would have the added drawback of working with threading locks, depending on the use case. So I am a bit wary about it.