It sounds neat, but I am uncomfortable with a central CA (Fulcio) and central log (Rekor). And I trust OIDC providers about as far as I can throw them. Granted, the whole point of a central audit log is to make misbehaviour apparent, but it still strikes me as the wrong direction.
I don’t have a useful proposal for a decentralised version, so I’m just kvetching at this point.
Also, neither X.509 nor JSON is great. We can do better. We should do better.