It is not uncommon for unhoused people to lose all their possessions, so even if purchasing multiple hardware security keys wasn't a huge financial hurdle, the recovery model I use (Yubikey on my keychain, two in my safe, mail one to my parents) falls apart for those on the margins of society. If email is an essential service in modern society, recovering access to it from some first principle of identity is essential. I don't have an easy answer for how to do that, but I also don't have a trillion dollar market cap.
That's true, we still need a good last-ditch fallback. FIDO could still save a lot of people from the hard login screen, the phone number gotcha, and the need to become literate in information-keys. Last-ditch fallback becomes a lot more viable at any given expenditure level if it doesn't have to serve as the primary authentication mechanism for half of the library's elders.
The CEO of Fastmail, a company which deals directly with the ID problem as an email provider with customer service, has made some insightful comments on this:
