Last I checked GM doesn't mass produce an inline-6 engine. The development and production costs would be insane, and the car would end up costing a fortune. Try to remember that the reason why car companies exist is so that they can make money. If they make a low-range Camaro, it's going to have an existing V6. Bottom-spec Camaros and Mustangs are not meant to me real performance cars, and they shouldn't be. The only reason you choose one over the other is either brand loyalty or styling preference. Saying GM should put a turbo L6 into the base-model Camaro is like saying Honda should put a high-output OHV V8 into the Odyssey, "so they'll outsell their competitors b/c they have better performance and still get decent gas mileage." It defeats the purpose of the car, so there's no point in doing it.