2) replacing pkg_resources with distlib (vinay posted a PR for this)
3) if not #1, pip installing setuptools on-demand when building is needed (this was the old plan I think for PEP439 until the recent changes, and get's us closer to the "MEB"s model)

to be clearer for everyone, #3 depends on #2, so that pip could install setuptools from wheel (without needing setuptools)