And your approach can be built into a system that does multi-threading away from Python, thereby achieving parallelism without requiring that Python supports it

And your approach can be built into a system that does multi-threading away from Python, thereby achieving parallelism without requiring that Python supports it as well. That's basically what all machine learning code written in Python does. It calls out to libraries that can themselves parallelize, use the GPU, etc. And then gets the answer back. You get parallelism without any special Python support.