The trouble spot with Superchargers is usually the end of the charge, not the beginning. The batteries can usually absorb energy rather quickly when at a low rate of charge. What is really painful is the last 10% where the charge rate drops line a stone.

What would be an interesting use of this idea would be to have 10% capacity onboard in capacitors. Once you get within 10% of the desired charge level in the batteries, you quickly charge the capacitors, which then trickles into the battery over time.

This might allow you to increase the overall charge rate for the car which would help reduce wait times at Superchargers.