Yes, ingima, I suspect a twin
Yes, ingima, I suspect a twin turbo on the 2.5 liter could push hp output well over 325 hp. Problem with turbo chargers is that they are weighty. A twin turbo on the 2.5 could add 150+ lbs to the weight of that engine and could be counter productive for a host of reasons.
We'll see what GM ultimately comes up with. I personally don't care as I all I want is a 6th gen Camaro with the LT-1 engine matched to either a 6L90 or 8L90 automatic transmission. But I agree with Patrick that for the purpose of marketing the car in Europe, GM needs a 300 hp + 4 cylinder in the car while keeping its weight around 3,600 lbs (or less).