What about a signed attestation of your identity based on your passport? I don’t particularly want a future where we need to present ID for any online service, but for certain high-risk services (e.g. financial services, medical records, government portals) I’d rather a proper identity system than cobbling something like this together.

As an aside, when traveling internationally it’s not uncommon to need to provide your passport information if you want to get a sales tax rebate. I’ve never purchased something expensive enough abroad to bother with it.