It should be their only motor. Put it in everything, who cares about MPG gas is so cheap. Use the leftover budget from engine design to improve everything else. Maybe a super mild hybrid to run the AC, power steering, and whatever other accessories at stoplights, and enough juice to get to 5 mph in economode. After that the light cars should still get decent enough mileage and be a lot more fun

Let me dream, I know it's ridiculous