They seem to be jumping ahead of themselves here. The Vengeance looks more like a 24th century ship. More like a Dreadnought Sovereign class variant.
Rememeber that scans of Nero's 24th century ship and weapons have been around for 25 years. One year prior to Into Darkness, an advanced Vulcan ship was spotted above the Earth, and left Nero's drill weapon in San Francisco bay. Scanning both ships as they lept to warp probably gave them some ideas about how warp fields are arranged in 2387. Apply that info to Starfleet designs and you end up with bastard child nacelles of a refit-Constitution and a Sovereign.
Meanwhile, they seem to have given up on the TOS era design style. Enterprise, even though its been restyled, still holds the TOS feel with the external Deflector dish, the rotating Bussard Collectors, etc etc. The rest of the fleet is still of the Kelvin era design.
Now JJ has Starfleet fielding huge ships with much later styling design. What does this mean for a third movie? They redesign the fleet to look like Vengeance variants? And so what do you get in the alternate 24th century, Enterprise J designs?
I haven't seen the movie nor even read the spoilers, but my impression is that the Vengeance is an aberration which will never be the norm for Starfleet.
Add in the real-world stuff: It had to look eeeeevil. Many of John Eaves' STO designs look absolutely monsterous. I think he was a good choice to design the manifestation of Starfleet's descent... Into Darkness!