Why why why?
Pay-by-bonk, I've used (once), with my Barclaycard card, and it worked OK.
But why on earth would I want to pay by bonking my phone, which needs apps/stickers/extra hardware and lets Google or whoever else sneaks an app onto my phone snoop on transactions, when cards work OK.
I'm always going to carry three things in my pockets: keys, wallet, phone. I don't want my phone to become my wallet (I'm always going to need somewhere to put cash, identity cards, scraps of paper, postage stamps, receipts etc so I need a wallet anyway) and I certainly don't want it to become my keys.