I've landed here after chatting with @brett.cannon.  I have a use case for this (making pex startup faster by bypassing pkg_resources) but I need to hack around the limitation of dlopen'ing .so's from zips.  Our idea was to have a zipimport subclass which doesn't return None from `importlib.util.find_spec()` when it finds a .so, but instead dumps that into some safe directory, and then arranges for a loader that knows how to load that.  It sure would be handy for this to be a zipimporter subclass. :)

I think Serhiy's patch predates the move to GitHub, so it's not a branch/PR.  I guess the next step would be to branchify the patch and then continue discussion over there.  Depending on my availability, I might do that.