This won't be entirely popular, because even today's low mass, twinned turbos do have some power lag, and they do make different and more annoying noises than a traditional big bore motor. Personally, I would drive a 2.0L gasoline or diesel turbo over a 3.0L naturally aspirated engine, if it would save me 20% or more on fuel, whatever noises it makes.
Another concern about turbos is their durability. I think that Audi, Volvo, Saab, and most recently Ford have proven that modern turbos are robust and can last for the design life of the engine. Ford's "torture test" YouTube series is entertaining, if you want to see a turbo engine severely abused.
The reason turbos help fuel economy is that at low engine load, say when you are cruising down the highway, your engine isn't using much of its power, the turbo isn't really running, and the engine is like a 2.0L I4. However, when you are accelerating, or otherwise making a high power demand, the turbo spools up and allows the engine to consume more air (and fuel), temporarily making it more like the 3.0L V6 you used to drive. Because the EPA fuel economy tests have a good bit of steady state driving, and idling, this variable displacement effect of the turbo really helps the MPG rating.
A smaller turbo engine, all else being equal, will also tend to be lighter weight than a comparable larger engine, which is another source of fuel economy gain.
Since turbos are cheaper than batteries and electric motors, the early CAFE gains are likely to happen through engine downsizing rather than hybridization. The next steps will probably be mild hybrids (start/stop, launch torque) coupled with downsized turbocharged engines.
