I read the "We're talking, we're talking" interview. I suspect, with only a little over a year to go before hitting the big screens, that there will be a bazillion rumours floating around. IF, they decide to put Spock prime into this film I sure hope it is more for just window dressing. Knowing Nimoy, though, I suspect that is exactly what they are 'talking' about.
I always thought Nimoy wouldn't do a window dressing style cameo. He dropped out of Star Trek: Generations because that is all his appearance would have been.
Who knows? Maybe he has changed his mind about that sort of thing?

Hmm... Just thinking out loud but perhaps this means SPOCK MUST DIE. Perhaps 'Khan' will defeat Spock this time. He'll die taking knowledge of other [potential] Earth destroying events with him leaving them without this advantage, and giving Nimoy a final discharge.