Identifiers are just attributes. If you want to attach a library card, US Passport, refugee id to a blockchain instance of your identity, you can inherit that endorsement.
In NIST speak, you can get a level 2 assurance level (good for most commerce) by collecting two strong identifiers or verifying one.
That does not solve the problem. If it did, we would have solved the problem decades ago
Case in point - pgp supports exactly that - you can have keys, which can have attributes which are endorsed by your key. We've had this since the 90's. It didn't solve the problem back then, reinventing the same thing but worse using blockchains won't solve the problem now.
In NIST speak, you can get a level 2 assurance level (good for most commerce) by collecting two strong identifiers or verifying one.