One major issue is that they are spectacularly complex devices that not only need lubrication and cooling, but the lubrication is constantly getting dirty; combustion byproducts plus whatever particulate matter the air filtration lets by end up on the cylinder walls and are moved into the lubrication system by the oil scraper ring.

Another issue is the very nature of ICE combustion which by its very nature (high pressure, high speed) it produces byproducts we don't want - plus the C02 that we also don't want.

Then there's the torque curve. ICEs are most efficient at particular RPMs (something I'm familiar with from designing race bike exhaust systems, using resonance and sound wave reflection to ''pack" overflow back past the exhaust valves to increase efficiency - long story, but for anyone interested the best book on this is "Tuning for Speed").

I will be desperately sad to see ICEs go from competition and high-performance vehicles, but have you driven one of the Tesla performance cars? It's not all bad news, although I'm worried for single track performance vehicles. Motorcycles are particularly bad at wind resistance, which goes up with the square of the airspeed. We may see fully faired electric motorcycle setups - like the Vincent Black Prince or the Ducati 907ie, but with a rear fairing, making the rider part of an airflow surface. Best case would be laminar, but I don't think we'll ever get close.

Interesting times...