If they don't, that's the best startup idea I've heard on HN in a long time. I mean, it's evil and everything, but you could make a lot of money probably. Government contracts would probably pay out too.
10 bucks says Palantir saw the idea and are working on the pitch deck right now.
The problem is convincing big store chains to put a new dollar barcode scanner machine in their checkout lines at every location, to do something that they have no trouble doing right now with credit card details, rewards cards, and bluetooth tracking.