I think you guys are thinking to much about this authentication method. It doesn't need to be QR or RFID, just a serial number embedded in a line of code or on the disc itself that is read first as soon it is placed in a console. It reports this embedded number to MS servers and ties it to your XBL account. It the game had already been used before it de-authorizes the previous owners account at the same time. If the previous owner fires up the game again once he's been de-authorized, he'll be promoted to either insert the disc or buy the game again from XBL.
I hope that is how it will work because it would allow me to continue to use GameFly. It could also provide a new benefit to GameFly-ers, you could still play the game after you put it in the mail and until a new GameFly-er receives the disc and installs it. Same thing could happen at GameStop. Your used game could go unsold for months and you can still play it, unless GameStop will be required to insert the disc in a console to de-authorize your account.
Nothing against the military but, I'm not a fan of allowing some people to not have to authenticate. I just think everyone should have to play by the same rules.