I touched up the PEP via PEP 691: touch up (#2668) · python/peps@f1af4a7 · GitHub , but it was mostly grammar and formatting stuff.
After reading the PEP, I’m happy to pronounce my acceptance of the PEP as its delegate! While I expect some things will get added to the spec in the future (e.g. application.json is going to get debated pretty fast once this rolls out, an optional url key for each project in the index object), the PEP covers all the details in PEP 503 in a JSON encoding and in a way that code can gracefully handle the transition.