Sadly, with the advent of Online Passes, this is a lot more plausible than it was last time around.
If they made it so that games are locked in 'demo mode' unless you have the right unlock key DLC (which can only be obtained with a single-use code) on your system, then used games become worthless.
It would be a monumentally stupid thing to do, but they have all the tools they need to do it.
--
"I'm Commander Shepard, and you're standing in the biggest library in Citadel Space. Look me up."