Lilja at Lilja's Library caught something on the video below that I missed:
Apparently King mentioned that he is working on a book called Mr. Mercedes. It's not supernatural, but a detective novel involving a person who drove a car into a crowd of people and then taunted the Detective who handled the case after his retirement. What started as a short story has turned into a 500 page manuscript.
On King's messageboard someone asked about it and the Moderator there said it would be at least 2014 before we see it, and that Mr. Mercedes is a working title that King isn't real happy with.
Very interesting. Video is below, the quote is at around 6 minutes.