Well, usually a long delay like this means that he's working on something big. There was a long delay before the Map Editor was released, for example. Given all the bugs that keep cropping up, he could be re-writing some large chunks of the program to handle things differently. Sometimes when you have too many problems you have to step back and find a different algorithm to do what you want with less "duct tape & baling wire".
That could also allow for some cool new options in the existing features of the game. He could also be readying drones or some other major new feature.