Old Kirk could have appeared during the mind meld in the first movie. It would have been brief but memorable.
The problem is, that would have called attention to the recasting, like including a clip of Sean Connery in Casino Royale.
Or including a clip of Katie Holmes in The Dark Knight.
They got away with including Quinto and Nimoy in the same movie because the age differential was so extreme (Young Spock and Ancient Spock) that you could pretend that they were the same character, separated by a long lifetime of experience. But a shot of Shatner might strain our suspension of disbelief . . . .
The conceit, remember, is that Kirk has always
looked like actor currently playing him--which is why Old Spock recognizes him on sight.