Anyone can run an OIDC system if they want. But PyPI is not under an obligation to trust an OIDC provider running on a random rpi3 in your basement. More than that, GitHub is "trusted" because we can be pretty sure they have an on-call staff to handle incidents, that they can reliably say "This token was provided on behalf of this user at this time for this build", etc.
Even if you standardized the more technical parts like OIDC claim metadata (which is 100% provider specific), it wouldn't really change the thrust of any of this — PyPI is literally trusting the publisher in a social sense, not in some "They comply with RFC standards and therefore I can plug in my random favorite thing" sense.
This whole discussion is basically a non-issue, IMO. If you want to publish stuff from your super-duper-secret underground airgapped base buried a mile underneath the Himalayas, you can use an API token like you have been able to. It will be far less hassle than running your own OIDC solution for this stuff.
Even if you standardized the more technical parts like OIDC claim metadata (which is 100% provider specific), it wouldn't really change the thrust of any of this — PyPI is literally trusting the publisher in a social sense, not in some "They comply with RFC standards and therefore I can plug in my random favorite thing" sense.
This whole discussion is basically a non-issue, IMO. If you want to publish stuff from your super-duper-secret underground airgapped base buried a mile underneath the Himalayas, you can use an API token like you have been able to. It will be far less hassle than running your own OIDC solution for this stuff.