I agree. And the idea of sharing a device but not sharing privacy needs high security-level that a face identification software would NEVER be able to reach.
I can put a photo of any member in front of the gadget's webcam.
And what about people who don't have the same outlook every they, e.g. shave their face once a week, or women with died hair etc.
And what about twins?
face identification needs confirmation.
It would be great having a gadget for the whole family, but nowadays I think the best way to recognition is the fingerprint-scanner, that could be on this tablet, anyway.