I think that there is a good chance it will get released early-mid 2013. He seems to write his books pretty fast, which is great for all his fans.
EDIT: It's kind of amazing how far in the future he's planned all his books. If you add up the next 9 Stormlight Archive Books, next 6 books that make up the next 2 mistborn trilogies, the next 2 elantris books and the next warbreaker book, you get 18 books that he plans to right. He also has so many series he plans to write that he hasn't started yet.