I think it's way too obvious that they will have a romance
How they can manage to truly develop one it's another matter though.
Let's face it: star trek had never been about romance. We already have a romance in the trilogy (Spock/Uhura) but it works because their relationship is very subtle.
With all the complains the writers received for one subtle romance, I cannot imagine how some fans would react if they add another
romance and if you get more subtle than S/U you have no romance lol
That said, I thought their main reason for having Spock/Uhura was so that for once Spock could be the one with a romance instead of Kirk. It sort of challenged the cliché that Kirk always gets the girl. It also was a reminder that this is another reality and their
trek. If they have a K/C romance now it will basically contradict that idea and the reason why they made that choice.
Now, I might be biased because I prefer Spock as a character and I don't want the movies to get turned in the Kirk show again frankly, but I think a romance with Spock is much more interesting, less predictable and more fitting with the theme of star trek (since he's half alien and the pair is both interracial and interspecies) Not to mention you have a legit pretext to make their romance subtle since he's a vulcan and can't get turned in the sappy boyfriend.
A Kirk/Carol romance wouldn't give me anything new. I also fear that it would unbalance K/S as protagonists all over again and not make them so equal like they should be. Kirk already has enough relationships to develop on screen: Spock, Bones and Uhura. You might even add Scotty. Plus you know know that every movie will have a scene where he's making out with some girl you will never see again.
Spock has basically only the Uhura and Kirk relationships and I'd hate to see his character development (along with the other characters like Bones, Uhura, Sulu and Chekov) get sacrificed only because they decide to add yet another connection for Kirk.
Even a Kirk/Carol friendship (I've read Orci saying that it was their original plan for the first movie) would be redundant now that they have Kirk/Uhura anyway.