Yeah - that kinda rings true a bit and kinda lends a bit of doubt. Unless they have some pretty amazing 'make-up' and cosmetics to make him look like a young Spock again.
As far as I know with the whole Elvin thing, even beyond Tolkien's versions. Elves never age in appearance but just fade and vanish.
Mortals get swallowed up by that Black Hole at the centre of the Galaxy you could say.
But Elves 'drift away' into the void - never to be seen again.
Surely though, Nimoy will only be a 'guest' appearance, with his 'ears'. Nothing substantial in the movie. Chuck Yeager appeared in The Right Stuff which was based upon his life a bit.
I'm trying to guess what part he could be involved in and I can only think of the last Hobbit Movie via Thranduil's kingdom.
???
...the whispers are getting more popular though. Nimoy himself is not confirming ...or denying the fact.