Considering he's not written anything more than what is out this year (and maybe something for next year in the background) we have no idea. This year's books include:
* The Rithmatist - 14 May
* Steelheart - 24 September
* Words of Radiance (Stormlight#2) - nearer Christmas
The Bibliography page on the wiki holds our most up-to-date infos. It has been mentioned (a while ago, this may have changed) that he aims to do 2 Stormlight books every 3 years, and he'll be taking a break at Stormlight#5 to write the second Mistborn trilogy. This is along with a few other shorter books (like Emperor's Soul and the Alloy of Law sequel, Shadows of Self, slated for next year) in between. I think he usually aims to release at least a big book (Stormlight, Mistborn) and a smaller one each year. It is unknown when he wishes to start the last Mistborn, but it's likely to be after Stormlight has finished. There were also rumours for the sequel to Elantris for 2015, its 10 year anniversary.