If I am in charge of Paramount I would be pushing for the earliest possible release date, no point in hanging around waiting for JJ. Christmas 2015 should be the date. Hobbit is finished by then and the new Avatar sequels will not be ready either. Christmas 2015 is the best date for Trek.
It'll be 2016, simply because that's the 50th Aniversary year.
They can make more from marketing it as the 50th Annivserary of the franchise than the 49th.
They can make it for Christmas 2015 and then do something else for the anniversary like a spinoff movie, new tv show or even film two movies back to back and have part 1 in 2015 and part 2 in 2016. Doesn't have to be 2016.