The notion that car/automotive engines are not up to standard for aviation use is now incorrect. Austro on the Diamond DA62 uses a 2 liter diesel engine made by Mercedes. The block, crank, conrods and pistons are unchanged form the car version. Todays modern automotive engines ith gasoline and diesel are pushing out hp and torque numbers unimaginable 10 years ago in consumer engines. Just look at Mercedes new 4 litre V8 in the AMG GTS. That specific power level was F1 territory 20 years ago.
The engine you buy today from Continental or Lycoming, while at face value looks unchanged for 50 years, the detail design and metallurgy means the engine is vastly different from its predecessors. 10 years or more Continental offered a blue printed line of engines at extra cost. That standard is now the norm.
However, diesels will ultimately kill of spark ignition engines for aviation, then they will be ale to standardise on 1 fuel type for the whole of aviation. Jet fuel.
Interestingly though Mazda has been experimenting with a compression ignition gasoline engine with a compression ratio of 18:1. It apparently has some super fuel injection system.