From the WoW's dev blog is clear that the festivities will begin on November 21st until January 6th. There will be again new present for all (re)subscribers in the form of Molten Corgi minipet. If you manage to get to the new level cap then you can play through new raid Molten Core.
What is not so possitive is the fact that the new PvP season and the normal and heroic versions of Highmaul raid will not open until December 2nd.