> Python's GIL inhibits parallelism within a process, and the workaround of multiprocessing and shared memory is awkward, has inconsistencies between platforms, and loses performance

Well, imho the biggest problem with this approach to paralellism is that you're stepping out of the Python world with gc'ed objects etc. and into a world of ctypes and serialization. It's like you're not even programming Python anymore, but more something closer to C with the speed of an interpreted language.