How do you verify the entities that are registered on the chain are who they are supposed to be? It may show a commit log of Citizen X voted in a certain way, but how do you verify it was Citizen X that actually voted or that they even exist?
Have they told you about it?
I'm not sure what the choice of media has to do with anything.
Who has told me what about what now?
Biometrics, seriously?
Biometrics are only a one-time proof when eg you are issued a token. They can be replayed later and can't be used anywhere except where there's a physical security guard preventing tampering. And even then you trust the security guard.
Obviously you use your device, and you can lock it with a password. You can use two factor authentication.
It's straightforward, really. You sound like identity has never been solved electronically.
If anything, holding a physical paper id document is far less secure than a personal device with your private keys in the Secure Enclave.