I think it's..... possible that it could actually happen. From a marketing perspective, putting aside the fact that it would make some people's heads explode for the alleged 'wrongness' of having the Borg in the TOS era, it would be a no brainer to use the Borg because, like it or not, they are one of Star Trek's most identifiable things for a broad population. Just like Khan. And the bottom line to those marketing guys is just being able to put the Borg on the poster so that people will go out and buy a movie ticket.
From a personal perspective, I hope it doesn't happen. I hope they can be more original, even if that means giving us a new villain from an already established alien race, just as they did with Nero the Romulan in the 2009 movie. Maybe the well-worn Klingons? Or maybe even give us a villain who isn't identifiable by his/her association with a past Star Trek race..... a brand new face. I mean, it can happen, right?
Or maybe they could find a middle ground, and throw a curve ball into the mix: a villain from the Prime Trek universe who has already been established as having actually existed in the TOS era, but who were never actually seen
facing off against the TOS crew, thus satisfying all the above criteria. The 2009 movie clearly stated that Cardassians were known to this version of Starfleet's finest..... maybe make the villain Gul Somebody-or-other, and have our first chronological experience of Starfleet-versus-Cardassia?
If Star Trek Into Darkness established one thing, it's that the DS9 era (Section 31) could be a particular gold-mine for the writers.