I think its existing behavior is because it doesn't have access to a list of recognized timezones.  As you say, this could be fixed by PEP 431.  It could also be fixed by adopting the "email standard" timezones (see email/_parseaddr.py), which is a def-facto standard.

Regardless of whether something is done to expand the number of timezone it knows about, though, there's a current doc bug that should be fixed.  If someone wants to advocate for expanding the timezone list, that should be a separate issue.