I voted for December 11. I think Blizzard will want to get it out early enough before the holidays to have time to fix the bugs that arise, so that they don't need to work through Christmas. I find a Christmas day release highly unlikely.
They could push it back until January, but I'd be disappointed if they did that. It would really take the wind out of their whole "deliver content faster" mentality. My guess is that by mid-late December, most normal mode raiding guilds will be accessing Terrace of Endless Spring (which is short and, as far as I can tell, easier than the other two raids - on normal mode at least), so it'll be a nice way for Blizzard to ensure that there isn't any kind of gap in the content that players can do.
Also keep in mind that it will take some time to get into the Brawler's Guild for the masses, so if they just put it out in late January or something, there many be many players who will feel they have nothing to do while waiting for Brawler's Guild access.
Also I think Patch 5.2 (new raiding tier) in early March. The raid is probably already well under way, and I can only hope it's not a small raid.