Probably staring down the Klinks? Not sure if it could be the Romulans since we know nothing about the Romulans in this timeframe other than they got a hold of some Narada technology.
One of the novels did have a borg-esque antagonist killing people, taking samples, talking about species xyz123 and talking of "assimilation", ultimately being a cloud of nanites. I found myself groaning.
I want to see them re-treading old ground from the original series because, again, It feels like all that was abandoned when next generation came out. I want the Tholians and Gorn back as main antagonists alongside the Romulans and Klingons. I want to see new takes on some of the bizarre aliens and things seen in the original (The Talosians, the Vians, the Doomsday machine, The lights from Zetar, the Horta, Nomad, and so on).
Alice Eve mentioned Charlie X, but I'm not sure if I would want to see that. Mostly because I'd rather see them doing other things.
I think one of the motives of the next movie would be the consequences of the destruction of Vulcan? It was something left hanging. My guess though would be on going back to the impending conflict with the Klingons, since it's going to happen whether Starfleet prepares for it or not.