I think Enterprise wouldn't recieve this refit, being assigned relativley close to home as of Season 4, but I could see the NX-class ships that are planned on being sent into deep space recieving that sort of refit.
I know Doug Drexler, the man who designed the NXs, actually pushed for a secondary hull (and more TOS-like paintjob) to be added to the NX for Season 4, since they had to refit it after the whole Expanse mission anyway.
He's working on a TOS-ified, secondary-hull-added NX for the 2011 Ships Of The Line Calendar!