In one of the later posts, the OP writes that the homeless will lose any physical thing after N weeks. So what kind of 2FA would be homeless-proof? I don't see a solution. Also, fully acknowledging Google and other bigtechs 2FA is far from ideal: The other thing is, we want at the same time Gmail to be unhackable against best hackers and state sponsored adversaries for the billions of users, including high profile di…
If they truly can't keep anything on them, someone who recognizes them needs to represent them. (A locker won't do - they'll lose the key.)
And if they have no friends they can trust (which is likely) then it probably needs to be a government worker of some sort, who has their photo on the computer.
I mean, unless you want to have retina scans to log into library computers or something. Or really reliable face recognition.