Amazon app currently already has barcode scanning. My guess is that they are replacing POS with app. If you think about it no one needs those arcane point of sell machines because smartphones can do scanning as well as payment processing. The only thing left is detecting unscanned items which is fairly well solved problem using RFIDs. May be later can be combined as well with measuring weight of person identified when entering.
This is brilliant as-in how no one else thought about it. Lot of small shops have limit on their open schedule because of staffing issues. I am assuming Amazon will set up few experimental shops and then sell technology to other stores. This can certainly revolutionize retail if they persist on executing right.