Without Shatner, Star Trek will die a merciless death. You don't kill the goose that lays the golden eggs, when will people learn from their same mistake. It would take very little to bring in Bill as a retrospective figure in the plot as well as keeping everyone else present and accounted for. He could make comments like, " I sure hope he (the young Kirk) doesn't do what I think he's going to do." It would be fun and entertaining as well as forfilling to the theater goers. WS isn't going to be around forever, take advantage of an opportunity to include Bill along with Lenard. The two really are joined at the hip. All fans, young and young-at-heart, would be very grateful and show their gratitude in cash. Its the logical thing to do.
I think most people disagree, but you're certainly entitled to this opinion. Shatner's end in Generations was fitting for me... is they're going to bring an old spock into the picture and likely come up with some kind of time travel plot--- having Kirk, who has now been lost in the Nexus and killed-- doesn't make much sense. Spock is still alive
well into the 24th century.