I admit I really like the Picard on sabbatical idea. I just don't see how you'd ever get something like that past the suits.
Yeah, it would've taken something miraculous, like Spielberg offering to direct such a movie only, and Stewart standing by him. Or Stewart offering to do it as a TV movie for cheap. Would've probably hurt the feelings of the rest of the cast, too. "We all not good enough for you? Shouldn't this sort of story be a novel?"
There's no reason for Uhura and Chekhov to still be on the Enterprise
during the late TOS movies. At a certain point, the actor-character dynamic overshadows in-continuity logic.