I am not so sure. The laws of physics apply the same now as they did before, and Diesel and low octane mogas struggle to provide sufficient power, efficiency and light weight.
These are three things a GA plane needs, and so far JetA burning diesel and turbine do not tick all the boxes. Nor can low compression mogas burning.
As Walter has mentioned above, these old technology engines still lead by a long way when you boil down the hard facts of what a GA plane needs. When you look at it, this is why we have had piston high octane burners for so long.
Invent a few new laws of physics, and it may be different.