From the sound of it it doesn't look like we'll see Zachary Quinto reprise his role as Spock in any more Star Trek films after J.J. Abrams' Star Trek Into Darkness. It seems like he feels he's outgrown the part, and is ready to move on. The actor recently did an interview with EW talking about his character in American Horror Story: Asylum, and during the interview he mentioned that he's ready to...
"... go in a different direction" with his career after Star Trek Into Darkness hits theaters next summer. "It's like an era of association with certain roles - a specific part like Spock, or a kind of part, like Sylar — is coming to an end."
Maybe I'm looking too much into it, but it sounds like he's ready to put away his Spock ears. Not sure why... any actor would kill to get a chance like this in their career to have a steady acting job making awesome movies. I think he makes a great Spock, and I hope he isn't finished yet. It would be hard to see another actor in the role. After all, we are used to seeing one person play Spock for a long time. Leonard Nimoy played the character most of his lfe, and I think as fans we just expected Quinto and some of the other cast to do the same. I also do understand that he's an actor and he doesn't want to play Spock the rest of his life. I guess it's something we'll just have to accept and see what happens if he doesn't come back.