However, Tor have decided that three books is the way to go (this isn't entirely set in stone however) and the first subvolume, called THE GATHERING STORM, is due in November with the other(s) to follow at one-year intervals. And apparently there won't be a US hardcover release. And the US cover is horrendous:
I have to say that this was pretty unexpected and rather barmy news. Unless Sanderson has decided he needs 900,000 words or something, there is no real need for the book to be split in three.