The other thing I should add is that I posted in response to the line 'No script ever put Spock and McCoy at the heart of the action.' I can certainly understand why, for many, many reasons, the ultimate shooting script, or even the second or third drafts, didn't have them in the thick of it. I was just surprised by the fact that no-one ever tried a first draft with them in it, just to see how it worked.
It goes back to what I said earlier, about Nimoy's problems with the script and the rewrite he wanted in order to direct the film. Sometimes writers are so close to something that they can't see its problems. And that's the issue with
Generations. We can look at the film and see all the dangling things that would have led the story quite easily into other, more interesting directions, but it never occurred to Moore and Braga to follow
any of those other directions.
Keep in mind that the first idea Moore and Braga had was to pit Kirk's
Enterprise against Picard's
Enterprise. The film's poster -- the two ships and the two captains squaring off -- would have had real marketing merit. But it ran into two problems. First, it would have been more expensive to make than
Star Trek VI (and the studio's goal was to make a film that was cheaper than
VI) since it would have had a massive cast to cope with. And second, they couldn't come up with a story that would paint both captains in an heroic light. Once they abandoned that idea, they came up with something smaller scale, and that idea was
Generations.
Yes, they could have put Spock into the 24th-century part of the film. Or Scotty. It would have been contrived, but if that was a choice that Braga and Moore had made, they would have come up with some sort of justification for it. (I think it would have been interesting to have Scotty in just the prologue and Spock in just the 24th-century part of the film. That might have seemed like contrived.)
I think the reason that Moore and Braga
didn't think of doing that is that they/Berman/Paramount wanted a film that was a
Next Generation film and that stood on its own in those terms. I don't think the film does stand well on its own -- it's mired in backstory from the television series -- and it's possible that the writers recognized that. So even if they had thought about putting one of the 23rd-century survivors in the back half of the film, they might have thought they were over-egging the story with kisses to the past. But I don't think that the thought would have occurred to them because they were so close to the film, at least not until they got script notes back from Nimoy.