Like SSH keys, where you manage your own identity and then share a public key to each instance that identifies you to that instance.
Like an identity client you could self manage if you wanted to. Make it optional, portable, and transferable. So you can choose to let a server host manage your identity, or migrate to a self managed identity.
If I had more time on my hands….
Conceptually a planned migrations should have a period of concurrent access to both the old and new accounts and it should be easy to publish a handshake to confirm the migration to followers to update contact info. That's my thought anyway. Something like keybase (does that still exist?) could also be used for similar sorts of proofs.
The way people used to handle this on Reddit is people would send a message from their old account saying "hey XYZ is my new account" and that seems sufficient.
Agreed. I think the barrier would be lower if I knew I could migrate my identity to another instance if the first one became sketchy or shut down or de-federated.
Instead AFAICT I have to choose not just what community to join and where the content will initially live, but also which of these random groups to trust with my identity indefinitely going forward.