There is a sci-fi way to get he Nexus into the New Universe but there is no time there - Kirk should not age in a place where time does not exist.
Now Kirk could have been living in the JJVerse for 22 years before discovery - or Spock Prime could use the Nexus asa gateway to get home
BUT what if Shatner does play an older time travelling nuKirk?? Here's the opportunity:
It could be William Shatner and Leonard Nimoy as Kirk and Spock on the bridge of the Enterprise in a new Starfleet uniform years on from ST16. Who said they ever left Starfleet? People could be worried that Bill could play jerk Kirk but in half a century the guy could mellow into a very decent officer. He could play the part as he always did.
I'll say it again: William Shatner and Leonard Nimoy as Kirk and Spock on the bridge of the Enterprise in a new Starfleet uniform
years on from ST16.
Sounds like a fitting 50th Anniversary gift to me!