Group control changes will have something to do with it for sure. I agree though. People are happy and not complaining. Just let things be. Why nerf anything at this point?
Buff more skills that suck (they didn't buff enough skills / passives last time) and give us an endless dungeon with increasing difficulty. done and done.
They can't just stop there though!
They should introduce Identify levels. For every rare that you identify, you'll slowly rank up your character's identifying skill and for each rank you can identify one extra item at a time. Eventually you can identify and then vendor the whole lot in one single click.
On a more serious note, I think it'd be pretty awesome if they had a way to enter the stats of your item you want to sell automatically into the search criteria on the AH. Also having the AH accessible through the internet would be killer though would also mean I'd become obsessed.
Switching between Acts while maintaining your NV would encourage people to play for a longer stretch.
Allow me to have the bonuses of my follower or something similar when I'm teamed with people. It sucks losing that Crit Chance bonus from my Scoundrel when I team up with friends.