There's actually no point to having Shatner in the new Trek, unless he's a character other than Captain Kirk (I'm thinkin Klingon). WHy? Because young Kirk (Chris Pine) was made Captain at the end of the first movie, so there is no torch to pass on, it was already passed by Pike to Kirk.
It also becomes problematic in terms of story-telling to include Prime Kirk. If he comes from the Prime universe, at what point in the Prime universe timeline did he get to the alternate universe? Since he dies in the Prime universe, he has to get back there. So then the entire storyline of the sequel will revolve around Prime Kirk needing to get back to the Prime universe, instead of focusing on the new crew and the events set in motion in the first film. The sequel, hence, becomes an entire appeasement for Shatner Trekkies that felt jipped by the exclusion of the Shat in the first film. I hope J.J. isn't stupid enough to go down this road.