This is far more plausible, where space is abundant outside the vehicle to keep a cache of supercaps to charge from. Especially if the usage pattern tends to b

This is far more plausible, where space is abundant outside the vehicle to keep a cache of supercaps to charge from. Especially if the usage pattern tends to be very bursty. But if the superchargers are (or will be) continuously near 100% utilization it's pointless, they'll need the current at the mains.