Caught up on distutils-sig this morning - I don't have any additional comments on Robert's and Nathaniel's draft PEPs except to say "I really like the look of where they're going, and look forward to reading the next iterations on them that take into account the feedback already received" :)

The idea of treating extras as subdistributions with their own wheel metadata also sounds promising (and analogous to building multiple binary RPMs from a single source RPM).

From an sdist metadata perspective, though, I think the right thing to do is to descope PEP 426 to just the stuff we *need* for the build system improvements, and defer everything else (e.g. JSON-LD, SPDX, richer dependency semantics, etc) to a future metadata 3.0 proposal (or potentially metadata extensions, or 2.x format updates).

The one major enhancement I think would be worth keeping is the metadata extension system (including mandatory extension support), since that provides a way to experiment with ideas that we may later standardise in 3.0.

I'm not sure when I'd have time to work on that myself though, so I'm definitely open to expressions of interest in taking a hatchet to the PEP. Nathaniel, Robert, perhaps you'd be interested in that as part of the build interface standardisation?

Regards,
Nick.