I don't think this is a big deal. Compatibility is a guess, wheel tags do not and are not intended to guarantee compatibility especially when the wheel was built locally for caching purposes and not intentionally published. Anything can happen during a build. PEP 517 won't change this.

So right now pip has an odd way of segregating its wheel cache per interpreter that involves obscure setup.py arguments. That can be fixed without re-tagging or asking the build system to re-tag wheels or otherwise interacting with the new PEP.