> Unfortunately for the user experience, those tokens typically can’t be cloned even upon initial setup. The practical result of this is that if you intend to keep a second token as a backup, you need to remember to register the backup token individually for each service you use your primary one for. This is unlikely if you keep the backup at home, and it’s downright impractical if you kept it in e.g. a safe deposit box.

This right here is what drives me crazy about most 2fa implementations (and now apparently webauthn). I currently store 1 backup token offsite, and carry one with me. The problem is - I have no good way to access the backup device (so I can add it to my account) without having both in my possession, which destroys its abilities as a backup token.

I would love to be able to somehow have 2 fido keys use the same key, but I'm not sure how that's possible without exposing the private key externally, destroying some of the device's security properties.