RRT 3 is being done by PopTop, expected to be out next year.
I have to believe that Sid is getting tired of doing CivXXX. In fact, I heard that he really didn't have that much to do with Civ3. I think Firaxis will come out with Civ4 within the next 2 years, and it will probably have Sid's name on it, but the next big Sid game will be something completely new.
Of course, I could be wrong, and Firaxis may redo one of the old Sid games, and put Sid's name on it. But I still believe if it really is a new project that Sid really is involved with, it will be totally new. He did mention in an interview last year when people were asking him what was next, that there were several of his original games that he would like to redo, with current technology, but most of them were owned by another publisher. I interpret this to mean that he is up to something totally new.