So the recent change to Google Wallet to let you use any card you wanted basically worked by creating a virtual credit card that acted as a proxy, and transmitting that card number using NFC. When the charge hit that virtual card, they would then process a corresponding charge to your real card.
It looks like they're going to give you the option of getting a physical representation of that proxy card.
One thing I'm curious about though is how chargebacks get handled with this system. Say I have the proxy card pointing at my Amex, I go buy something, and Google forwarded the charge to my Amex. Now for whatever reason I need to do a chargeback. Who do I talk to, Google, or Amex? How would that even work?