I agree, while the hybrid thing makes a lot of sense on a car where weight is less of an issue, I would not want to carry two engines in an airplane (unless it's a twin)
I do however agree that the GA industry is hopelessly behind the curve and I find it hard to understand why we are still sticking to carbs and aircooling (even Porsche had to move on).
There are a couple of promising developments going on though, Rotax abviously being one well proven and quiet solution. Another (less quiet) are the new generation of small turbines such as this:
PBS Velká Bíte?, a.s. ... Turbovrtulový motor TP 100
Sonex are mounting the jet version on their new sub-sonex