When I hear about "device-based verification" what comes to mind is a device that can be put into some kind of child safety mode, by parents who want to give their children phones or whatever. The device then "knows" whether or not its user is a child without any kind of biometrics or identification.
It has some problems and could case a lot of harm if it's badly designed, but it's the only method that seems close to workable in any conceivable form. Why is it never even talked about in these discussions?