Last time I checked Northorp and Grumman were still primarily aircraft designers. True, they operate Newport News Shipbuilding Co., but that is a manufacturer of Nuke Boats. Their expertise wouldn't get them much past the hull design since there hasn't been a suitable diesel-electric system since the '50's here in the US.
The major cost of new weapons systems is the design work. That is why there was so much todo about the Army scrapping the Crusader Artillery System -- the design was already paid.
Besides, conventional boats don't have unlimited power generation capacity. They must therefore have smaller displacement, crew size -- everything. You can't just take the hull plan of a Nuke and slap a diesel-electric plant in it. Just imagine trying to mount a snorkel in the Conning tower layout.
Also, I never implied that a nuke design be adapted for this requirement. Obviously, this would be something new for NG/NNS, but certainly within their capabilities.