This is the first place I've heard about a "what you can do" authentication method. It sounds intriguing. I wonder if I might be able to register a bunch of unique identifiers with some agency or other, in the event that my ID gets challenged and I some day have to prove what data belongs to me.

That's the next challenge, I suppose: Linking ME to MINE.

but what if I have a cold?

Ah, right. Or a broken finger, or a sore knee, or a momentary bout of forgetting how to play "Danny Boy". (It happens.) This is a good point.