I don't see the AR applications even being the most interesting part of this. A private facial recognition database coupled with "this person's name and a note to self" would be immensely helpful in a lot of situations -- I have bad facial recognition (not full on face-blindness, but inconvenient) and it would be neat to be able to hack on this a little bit. This would also require a camera of some sort, but I'd rather have that not be integrated.

Possibly even "real-world closed captions".

A tap for clock/calendar function would be handy.

Morse code (or other silent, maybe subvocal?) "telepathy" would be interesting as well.

I don't know how convenient or awful these would be in reality, but if the cost were not exorbitant and you weren't locked into a proprietary app ecosphere then it definitely seems like it would be worth a shot.