Star Trek director J.J. Abrams has made it no secret that he would like to have William Shatner appear in Star Trek 2, even planning a lunch to talk with him about it.
At a recent unveiling of a wax figure of Shatner as Captain Kirk, Shatner said that his participation in the sequel is entirely up to Abrams.
I have no plans, because I don't make those plans. JJ Abrams has my
fate wrapped up in his two little hands. I would love to be in the next Star Trek, if he so thought that would be good for it.