I always thought the most interesting story that could feature Shatner as Kirk, would've been to place Storm Front
forty years later and in that reality Kirk, Spock and McCoy never escaped the 1930's from City...
. Archer would've teamed up with an elder Kirk who was now running the mission in Nazi occupied New York.
Before the timeline gets set right, an elderly Kirk gets a chance to step foot onto the NX-01 bridge and sit in the captains chair one last time.
That sounds fucking amazing. The more you think about it, the better it works. A faction in the TCW having taken advantage of McCoy altering history. He's pushed Edith out of the way, and been hit by a truck instead. She's nationally famous as a peace campaigner. The Nazis invade the US, and we're told Spock had been taken away for dissection... so Nimoy not required, leaving Shatner to play a broken 60-something Kirk discovered by Archer. Shift it forward in time to an alternate 1966 with a facist America versus Soviet Russia. Probably a Black Civil Rights underground and other ongoing resistance movements, instead of just Italian American Gangsters in NY.
No need to involve the Guardian of Forever. Obviously have Kirk hint at it just enough to piss Harlan Ellison off, with not enough grounds for him to file a lawsuit.