The problem turned out to just be inspect.getmodulename() still relying on the deprecated inspect.getmoduleinfo(), so I changed it to be based on importlib.machinery instead.

I did make an importlib API addition to do it though - the all_suffixes() function dynamically adds together all the suffixes relevant for the current process so it will pick up any modification post import, while still allowing code that doesn't care about module types to ignore the details of the different kinds.