> Absence of support for self-hosting, or for that matter for any non-proprietary service?
This has nothing to do with self-hosting, whatsoever. You can upload to PyPI with an API token; that will always work and will not do anything related to Trusted Publishing, which exists entirely because it makes sense for large services.
PyPI isn't required to federate with the server in my basement through OpenID Connect to be considered open source.
Absence of support for self-hosting, in the spirit of freedom 0 = OSD 5&6? Or, for that matter, for any provider whose code is fully open source?