Watch Shatner get pissed off about not getting offered enough money and tell J.J. to go fuck himself. Shatner has crafted an iconic and legendary pop culture hero/character but the actor himself can be a giant horse's ass and egomaniac. He could get offered Jim Carrey bucks and say no because it would fall $1 million short.
no offense, but he doesn't exactly look "normal," certainly not like a normal eighty-year old. he can also be rather ham-fisted.
i'm sure he'd pull off the kirk role with aplomb, but i don't think he'd want a cameo. and barring any more time travel/alternate universe/mind meld bullshit, i wonder why anyone would want to shoehorn him into a new star trek when nimoy already handed over the reins quite capably. besides, kirk already had his final moment in the sun in generations, and as dissatisfied as many are with his death, it gave a certain finality and resolution to his life.
with respect to shatner's kirk, why not leave well enough alone and let these new actors stand on their own two feet?
personally i wish only that shatner could have kept his ego in check when this film came out and avoided the appearance of discontent. it was unbecoming of him.