It also breaks .zip file distribution, which I'm fairly sure we do explicitly support by virtue of having "python36.zip" in sys.path by default. And the ".pyc-only in a zip file" distribution is *totally* busted :) (and also officially released for Windows...)

I'm dragging in an importlib expert to the discussion, probably against his will, since this is really a problem of "how do I programmatically discover what I can import without using os.listdir()". Hopefully Brett can answer that question and we can come up with a patch.