Wouldn’t that require running an interpreter in each thread? How on earth could that be a “sane multi threading model”?

>offer a safe path to concurrent programming

Uh, doesn’t Python support this already? Python has “concurrency” from async and parallelism from multiprocessing. What it doesn’t support is thread-based parallelism. What you’re suggesting (if I understand it) is an implementation of parallelism that is barely different at all from the typical Python parallelism approach of using multiprocessing to achieve parallelism.