This solution is going backwards... As almost entire world (I mean the world outside of the USA) accepts the card payments using the NFC standard the MCX here in America wants to introduce another, yet propriatery solution of payment. This is ridiculous... I hope all interested parties will wake up and walk away...
Pay could front-end a QR code-based payment method - but I'm VERY sure you'd be able to tell a difference. Not only is the payment interface different, but the way the transaction flows is also different.