On the Game Developers Conference, GameSpy managed to get an interview with Peter Molyneux, where he amongst other things admits to having plans for Black & White 3. Here is a spot from the interview:

Early development of Black & White 3 will begin in a few months with a small team devoted to developing a new engine for the game. The storytelling will allow more branching instead of a straight linear variety. There will be different resolutions to problems, bringing a slight RPG aspect to the game. "I'm incorporating what we are learning from Project Ego to enhance the game experience," Molyneux said. Full interview here!