I reckon the Elder Scrolls MMO might give WoW a run for it's money. Graphics wise it should hold a much higher standard than the much older WoW, even though that's not that important to me, I know it is for a lot of people. Skyrim was a big success with a ton of players, if they can get similar numbers for their MMO, it's possible they can knock WoW off the MMO throne.
On another note, I really hope we will hear some news soon about Blizzard working on Warcraft 4. WoW has kinda ruined the story for me, but it could still be a great strategy game. Warcraft 3 is my favorite game of all time.
They aren't working on another Warcraft. They already have a new project. Titan. We know almost nothing at all about it other than it is an mmo, it is entirely separate from every other game they have made, and WoW is supposed to still be going when it is released.
Titan is either the name of the project, the engine or both so it is likely that it won't even be named that upon release.