The last I heard was that they had been in London for a bit with Jeff Marx and had written a couple of songs for their show which is supposedly about mormons. I think they were over there because Jeff was helping and getting the Avenue Q production up and running in London. I am pretty sure that Bobby Lopez is helping too but I didn't here is name mentioned the last time. I don't know when they have this or hope to have it open but I think I also heard that Trey Parker and Matt Stone were working on two more movies: one being about a group of highschoolers and the second one was going to involve men in monster costumes attacking a city (It's their take on Godzilla monster movies)! With those two other projects going on along with this musical who knows how they are coming along; I am not sure what their highest priority is.
Have you ever seen Trey's musical Cannibal? If he scored the whole thing while still in college and wrote all the lyrics himself, he is damn talented. I love their comedy and trust in any musical capabilities they have. It would be great if they did more.