Folks,
There is one vital point missed in all this, the aircraft that are piston powered, as new build aeroplane, are built in small numbers.
If there was a real market for a "modern" piston engine with all the bells and whistles, they would emerge.
There have been a few tries recently, an small HP Jet A diesels are being built in small numbers, for the small number of aircraft, to which they are fitted.
A lot of money has been lost by the original developers.
Auto comparisons are just plain silly, not only because the operating conditions are so different, but far more importantly, motor car engines are built in the millions, justifying the development costs.
Tootle pip!!