I don't think it will sell as many copies in the long run. First of all All that... not only spanned 2 christmases on the charts, but also had big bounces from not just one but 2 big grammy wins, Superbowl halftime show, NBA performance, etc...
I think that it will fall by about 60% this coming week and stay pretty solid through the holiday. But if we don't have another big, high profile single or video or music awards, or tv appearance or something, I can only see this album selling 3 to 3.5 million. I don't think that this album will span 2 holiday seasons either.
but hey, that's still great sales - and I hope it does go further. I think it deserves to be heard by as many people as possible.