> Seems like everything that would benefit from it is already written in highly optimized native modules

Or by asyncio.

I'm pretty ignorant about this stuff but I think asyncio is for exactly that, asynchronus I/O. Whereas GIL-less Python would be beneficial for CPU bound programs. My day job is boring so I'm never CPU bound, always IO bound on the database or network. If there is CPU heavy code, it's in Numpy. So I'm not sure if Gil-less actually helps there.

asyncio is unrelated to the parallelism prevented by the GIL.