Bornakk, who apparently looks like Abe Lincoln, has revealed that Naxx will be an "entry level raid dungeon" in Wrath of the Lich King, and EU CM Vaneras adds that unlike Kael'thas (who exists in two places at once ingame), it will be moving whole hog up to Northrend -- the 40 man dungeon that we have now will no longer exist.
Very interesting. Unfortunately, we're not quite clear on what "entry level" means -- it seems unlikely that Naxx would be a level 71 dungeon (or that there will be any "raid dungeons" before level 80 at all). And the fact that he uses the word "raid" definitely means it's either 10 or 25man, then, though whether it will be the new Karazhan or Gruul remains to be seen. Bornakk also says that attunement isn't solidified yet -- a lot of players are hoping that all that Argent Dawn rep doesn't go to waste, but he says it's a matter of balancing "special quest lines" with opening up content to many players.
Finally, the Ashbringer gets a mention -- apparently it will be discussed in the next Blizzcast. It's great to finally be hearing some official information about Wrath of the Lich King, vague as it may be. Hopefully there's lots more to come, sooner rather than later.