I'll be the first to admit this could be nothing but a rumor, but over at the trivia section of IMDB is this gem for Generations:
We all know the scene in question and it would have probably been cute. Of course had Takei returned as Sulu we probably wouldn't have gotten his daughter in the movie. It just seems like a dumb reason to me...of course it makes sense after reading his autobiography and seeing how much of a stick up his ass he had when it came to Shatner.
The producers asked George Takei to come back and play Sulu one more time, and take the helm of the Enterprise-B. But Takei refused because if Sulu had taken the helm, it would have meant temporarily reducing Sulu's rank, so that he could serve under Captain Kirk again. He felt that Sulu had worked too hard to earn his command to allow even a temporary reduction.
We all know the scene in question and it would have probably been cute. Of course had Takei returned as Sulu we probably wouldn't have gotten his daughter in the movie. It just seems like a dumb reason to me...of course it makes sense after reading his autobiography and seeing how much of a stick up his ass he had when it came to Shatner.