You wouldn't need the flywheel or capacitor in the car if that battery really works the way they say, and doesn't actually explode when you hit it with 150,000 watts.
I've yet to hear a good reason for not swapping batteries in electric cars. The battery can be swapped quick and charged slow, tested to see if it's worth a damn or needs to be sent to recycling (all automatic). Standard size batteries, small car takes one, big car or SUV takes 2, truck takes 4 - 6 or whatever.