Thanks for the great feedback - Nick, Donald, Paul, and Richard (off-list).
I am totally fine with focusing on PEP 458 and applying the final coat of paint on this document.
There's a lot of background documentation and technical details excluded from the PEPs (to avoid turning the PEP into a 15+ page behemoth), but I do agree that we should explicitly cover some of these implementation details in PEP 458. Subsections on the exact format of metadata, explanation on how metadata is signed, and how the roles are "delegated" with the library, still remain. As Paul as indicated, terminology can also be improved so as to be more readable for "non-experts."