So, you can see the first teaser now on Youtube, by the way. Cumberbatch's character talks about returning - I'm putting my money on Khan.
EDIT: The Japanese trailer has what looks to be an awfully familiar scene (spoiler if so) at the end. Plus I just noticed that it is clear that Cumberbatch's black uniform certainly has that much-reported black Starfleet insignia.
I would think that the old Spock would be sensible enough to follow the temporal prime directive in those situations. Having said that I don't know if JJ Abrams would do the same.