As reported by MTV Movies Blog that is.Apparently Frank Marshall has told MTV News that he is still open to the idea of another Roger Rabbit film, after the idea was nixed in the mid-90s due to cost-prohibitive special effects.
With Disney Animation being overseen by John Lassater and going back to traditional animation, it may be possible for such a film to be made now....?
http://moviesblog.mtv.com/2007/12/11/roger-rabbit-sequel-still-in-the-offing-stay-tooned-says-producer/
Although I love the original, I would hate to see a terrible sequel that would ruin Roger Rabbit's career for a new generation. There has been talk about using CG props and characters, and I'm not sure that would be a great idea.
Here's an article that explains the "history" of the Roger Rabbit II plans as they were during the 90's:
http://www.filmbuffonline.com/Features/RogerRabbitII.4.htm