Supporting sdists and source trees in PEP 665

Are there things we need to change (instead of add) in PEP 665 to make supporting building from source possible? I’d much prefer we move all conversation about strict additions (in other words, changes without causing incompatibility concerns) to an entirely separate PEP and thread. It took us six years and 500+ messages to come up with PEP 660 (also noting that universal concensus was not reached even after all that), and I hope we could be able to use the lock file’s equivalent of PEP 517 first, instead of having to wait for everything to be ready in one shot.