The US Littoral Combat Ship is based on that concept, but screwed it up, resulting in what is basically an overpriced fast OPV. It is a good thing later versions of the LCS will have the armament of a "proper" frigate.
Have they picked a final configuration for the LCS/Frigate yet?
Build ten ships. Two are combat fitted, Two anti-mine warfare, four narc/CG outfitted. Ratings train on other fit out when on shore.
When needed change modules as the situation warrants upgunning as many as possible before you need to deploy.