One interesting thing of note is the spec for declaring extras explicitly reserves test and doc for listing the dependencies necessary to run your test suite and build your docs, respectively. So if we can toss in a way to specify how to do either we could get sdists which include PKG-INFO using a new-enough metadata version to be relatively self-contained when it comes to this stuff.
I also wonder if build tools should consider stripping out test and doc from wheels which don’t contain the test and doc directories necessary to actually work?