Re: Orci, Kurtzman and Lindelof should not Return.
As for Vengenance being top secret. Marcus had a model of her on his desk. I'm not 100% certain that she was completely top secret beyond her modifications. The class might have been developed for some other use (example: Long range explorer) and Marcus hijacked the project to build his super ship.
This almost certainly has to be the case. There's no way they could've went from drawing board to working prototype in less than a year. Not on a ship that large and full of new technology.
"I tell you what you all need, you need to take a thirteenth step, down off your high horse." - Hank Hill, King of the Hill