From what we've seen of the teaser trailer the Enterprise will probably have a level of changes in-between that of Vector's Enterprise and Gabriel Koerner's Enterprise(the one being used on Star Trek Reborn). It's quite obvious that it's not going to be completely redone so I don't understand why we're are still arguing over whether if they should create a completely new ship design or not.
I would also like to point out that Moore's re-imagined Battlestar Galactica show with all the radical changes he did to the story and characters still kept the original design of the ship. I'm guessing it was updated a bit but overall its basically the same design that they used in 1978.
Also, today's navy ships and air craft carriers are pretty ugly when compared to cruise ships so maybe the same parallel exist in the future in space.