pretty good theory assuming they don't completely change the styling, which they likely won't. though it is a possibility.
as for the engine, I'm also thinking it may possibly get the C7's motor, which is even better.
the problem with that is though, that nobody's biting on the Caprice Interceptors, mostly because of the asking price, but also because of the Country of Origin issue (which is also a factor in the price, as it was with the GTO and G8.) So the innocenti will probably never think, "oh, that's just a copcar." they'll just think its another idiot speeding along in a sports sedan. granted, that is the one GM car that would be able to do it as below-the-radar as possible, but there's too much woring against it.
I'm thinking perhaps the best car for the job, going on your theory of blending in with the cops, is likely going to be a Dodge Charger. If painted black, and loaded with extraneous antennae, it would certainly look the part of an undercover/unmarked police car. few people would think twice about it being anything else if it speeds past them. Also, there's the technicality that you won't actually be guilty of impersonating police because its not loaded with lights and sirens (or have the word POLICE brazenly emblazoned across it like the Bimmer did).
On the flipside, the Charger is rather portly, and at full tilt, the gas mileage is going to be a problem. weight saving measures will need to be taken.