Are the specifications in the PEPs above implemented somewhere
or are they only 'specifications'?

The Packaging User Guide is maintaining a summary of the relevant PEPs that gives a brief description of the "user impact" and "implementation" (i.e. whether projects are actually implementing any of this).
https://python-packaging-user-guide.readthedocs.org/en/latest/peps.html
For those working on the various projects, please help keep this up to date.