[ensignavenger]

I find that the essayist way to handle backup keys is with a printout of 10-20 pre-generated auth codes, which go in my safe. Much easier than having a backup hardware key I have to remove and then replace from my safe, each time I need to add a new service service.

[JshWright]

Which is great if you have a printer (and are near it when you're signing up for the account, and remember to do it, and remember to put it in your safe, etc...). Just because it's the easiest way currently doesn't mean there isn't substantial room for improvement in the usability of passwordless systems. Most users aren't going to go to the trouble of printing something out like that.

[eco]

You can also use a pen though your point on ease stands.