I would love to throw a twist in the WoW machine. I'd like to see an option for Dual class. You get two classes, right outta the gate, BUT, you can only have one spec in each class. So, you are still technically a Dual Spec, but with a twist. Also, your new class(es) would still have to keep two sets of gear. You could be a rogue/mage, but you better have a set of cloth gear and leather gear for him/her. You want to play a Blood DK/Fury Warrior? No sweat. Ready to be a Destro/Brewmaster? Go for it.
Just another random thought in the endless cycle of possibilities in the game.