Not all 3D movies always have 3D trailers. It is quite possible that there will be a 2D version of the trailer (to be shown in 2d theaters).
I mean, there will be TV commercials in 2D (maybe even a big one during the Superbowl, like last time), so why not a trailer in 2D?
...And, yes. Abrams said he would have preferred the movie to be in 2D, but Paramount overruled him.