Debuggers will have to work around this in past Python versions that they support (which still includes Python 2 for pretty much all of them), so this is solely about resolving the inconsistency for the future. No point rushing it for 3.8 specifically.

(The most likely immediate workaround will be that, instead of invoking PyEval_InitThreads on the main thread via Py_AddPendingCall, we will simply use the same facility to exec "import threading" on the main thread.)