I've dreamed of something like this too. I think it fills a good spot especially smaller transactions. I see parallels to the nordics bankid+swish, bank issued

I've dreamed of something like this too. I think it fills a good spot especially smaller transactions. I see parallels to the nordics bankid+swish, bank issued id/phone payment system. It's flawless in execution but both the id(!) and the payment part carries a cost picked up by the person accepting money (about $0.12 for each, very bank like). With your way of doing things none of the parts has to cost anything at the reasonable expense of potential double spending.