Well, I really hope he doesn't want to due to typecasting, because incase he doesn't realize pretty much most of his roles are exactly the same, an arrogant jerk. Ghostbusters of course, Groundhog Day, Scrooged, Stripes, Rushmore, etc. etc. long, long, long list here. What About Bob and Ed Wood are the only ones I can think of that he's shyed away from his Venkman. Infact when I was thinking about it, all they needed to really do was call him Peter Venkman in all his films.
Ghostbusters, Ghostbuster 2, The Adventures of Peter Venkman - Business Exec. Christmas Style, The Further Adventures Of Peter Venkman, Newscaster Trapped In One Day, this is fun, try it everyone lol.
But besides the point, I agree with the idea that he doesn't want to share the GB limelight with anyone else, unfortunately. It just proves the point of the jerk that people in Hollywood really say he is.