We know what the Borg are. We know what they're going to do. We know pretty much everything there is to know about them and we've seen it all. I for one would be decidedly less than excited about going to see another Star Trek film about the Borg.
But we aren't the general audience. They haven't immersed themselves in Trek lore the way that we have and likely most have never seen the Voyager and Enterprise episodes. It will have been twenty-two years since their sole big-screen appearance when Star Trek 2016 is released. Plus, the Borg are one of the few Modern Trek assets that has at least some name recognition amongst general audiences.
From a marketing and ticket-sales standpoint, I think Kirk vs. the Borg is a no-brainer. Question is: do the current Powers That Be have the chops to pull it off?