Looking at the patch, is there any reason it doesn't get rid of the
current _PyModule_Clear() implementation to replace it by a call to
PyDict_Clear() followed by PyGC_Collect()?
(the call to PyGC_Collect could be disabled while finalizing, because
there's no use calling it as many times as there are modules to be
disbanded)

The major annoyance with the current scheme is that, at interpreter
shutdown, some globals you want to rely on in your destructors suddenly
become None.

About what to do of gc.garbage at shutdown, there was another proposal
in #477863.