Question: If someone had such a flywheel, could it quickly transfer a full charge to an electric car?
The added mass of the flywheel would, of course, make the entire vehicle that much heavier. It’s been tried on city busses, but that’s a much larger vehicle. The flywheel has to be pretty friction-less. Jouncing around on a typical roadway might not be something that you’d want to do.
It is also going to want to stay in its original orientation. The gyroscopic effects would probably be immense.