What with all the recent talk of what else might be in the expansion, I am starting to think it may launch sooner than that. It depends, in my opinion, on when Sunwell Plateau launches and if we can expect them to have learned from the original launch of Naxxramas so close to Burning Crusade. In my opinion, I'd hope there would be enough time between the Sunwell launch and the expansion for more guilds to get to see the place in full, especially with the way we're told content will unlock there as people complete quests. So I wouldn't be surprised to see it in late spring/early summer, nor would i be surprised if it didn't launch before Christmas of this year.
Meanwhile, take a look at the two new monsters being unveiled for us today and get your speculation on.