I don't want to go too heavy on the negatives, but what's nuts is Python going for trust-the-programmer style multithreading. The risk is that extension modules could cause a lot of crashes.

My understanding is that many extension modules are already written to take advantage of multithreading by releasing the GIL when calling into C code. This allows true concurrency in the extension, and also invites all the hazards of multithreading. I wonder how many bugs will be uncovered in such extensions by the free threaded builds, but it seems like the “nuts” choice actually happened a long time ago.