Holy fuck it's true! From The Shat himself: http://comicbook.com/2014/09/27/william-shatner-confirms-he-was-contacted-about-star-trek-3-and-/
I was surprised to read that Shatner couldn't come up with any idea of how to get him in the film. I would have thought that he would have been one of the first to have an idea. That being said, if Orci has an idea that can get the two of them on screen together, I would to say to both Nimoy and Shatner - just do it the way it's written. I, for one, trust Orci enought that if he has a plan to get them into the current storyline, it's probably a good one and makes sense in the story that's been written.