What links those accounts is not special, it's OAuth2. I don't think there's anything stopping different groups from running open OAuth2 endpoints that just pro

What links those accounts is not special, it's OAuth2. I don't think there's anything stopping different groups from running open OAuth2 endpoints that just provide a PGP based identity service. I actually wondered why Keybase didn't start an OAuth2 endpoint, because it'd put a big dent in some of the services you described.