I'm kinda late to the party on this, but I hear on and off that Good Omens is in the works, and if that works out I could possibly see some other of Pratchets books becomeing comic fantasy movies, I know not quite in the genre that you are talking about, but it is a step in the direction that might allow them to do it without fear of imitating PJ too much.

The other direction I would love to see this go is if Gaimans American Gods is made into a movie after Good Omens. That could eventually lead to the possibility of Sandman movies, and that would surly kick much ass.