Too old, too fat, too late, no Shat.
Don't get me wrong... I grew up with Shatner's Kirk and he is my boyhood hero! But the man is too old and too far gone physically to portray Kirk with any sort of dignity any more. Plus the mechanism required to get him into the film - short of simply ignoring his death in GEN - would be the most convoluted fanwank imaginable.
I look forward to Chris Pine's portrayal and don't think we need to dwell on the franchise's past.
For the time will come when men will not endure sound doctrine. Instead, to suit their own desires, they will gather around them a great number of teachers to say what their itching ears want to hear.
2 Timothy 4:3