Earlier quoted context omitted.
Is there a solution for the fact that all of your accounts will be secured by the same "source"? Isn't this almost close to using the same password on every site? I realize a physical secret is better than a password, but if someone gets their hand on your little FIDO device, do they instantly get access to all your accounts?
The big problem with using the same password on multiple sites is that if any of the sites record your password (because of maliciousness or incompetence), they can re-use your password to log in as you on any other site. Using a security token is more like a password manager with random passwords everywhere than that (the attacker needs to get access to your password manager to get access to your accounts; it's not…
Does there exist FIDO key (other than phones) that require a password to "enable"? For example, when it's plugged into a new device, the key locks until you input some master password?