It's still nothing to do with X, and it's not certain that it would plug the "hole" that is being used here.
This "exploit" requires unfettered (or at least not completely throttled) access to the CPU and a way to send the spoils home via the network.
Would this actually be stopped with "lxc"? I doubt it'd do much to curb the CPU abuse, and network access is something games frequently demand (in something like this for e.g. leaderboards or a social sharing feature), so I'd bet that nobody would bat an eye.
Sorry, missplaced my answer. It was regarding the guy above yours concerning apps in general can create havoc to a system. I mean that using containers like lxc can create a sandbox.