That could have been great - not only could they have possibly gotten Nimoy as well, but it sounds like a much better story then going back to a marooned, older Mirror Kirk.... or even the twist that it was a warped version of the actual Prime Kirk that unintentionally created the Mirrorverse.Have "Storm Front" take place in a 1970's where Kirk and Spock never made it home after "City...". Kirk is running Edith Keeler's old mission in Nazi occupied New York.
That's how I would have done it.
Its always been headcanon of my own that during the momentary change in history during "City", the Mirror Universe was created as a spinoff of Nazi Germany winning WW2. So this would have been fantastic to me....