It would have been more realistic for Spock not to coincidentally return to his actual age.Provided they could have done so with a quality actor, could you have accepted a "new Spock" at the end of TSFS?
And would that of been the perfect opportunity to do so if it was going to be done at all?
In TSFS, Spock is aging at a accelerated rate that by the later scenes in the movie delivers us back to having Leonard Nimoy as Spock. However earlier in the movie we see a different actor as Spock. Please bear in mind that I'm not suggesting that that actor becomes Spock from that point forward.
Leonard Nimoy was on record as wanting to discontinue playing the character.
The scenario I am suggesting is that Spock doesn't age back to the approximate age he was when he died, but instead he "stops" at a earlier point, result in a Spock who would be about mid-thirties - early forties.
Obviously he wouldn't look like Nimoy.
The experience of being exposed to the Genesis effect and having his Kantra "re-fusioned" into his consciousness could be used to explain the new actor's take on the Spock character.
Any thoughts?
However no-one has every played Spock better than Nimoy and noone ever will. Even cute little boy Spock.
Aside from that imagine Shatner having to compete against a younger man.