Vision: you drive into a supercharger station in your Tesla RedDwarf (Gen V :o) and park over a charging rig. Two or more chargers automatically click into place. Some begin to top up your batteries while others very quickly spin up the cylindrical flywheels integrated into the car's battery platform. Within a minute or two you're off again. For the next 20 minutes, the flywheels are used to top up the car-batteries. For the remainder of the trip they're used in a way similar to eg. the KERS system in place of regular electric regenerative braking.
Is this vision realistic when you get down to the numbers and the science? One number I've seen floating about on the internet is an energy-density (on the lowish end) of around 100 Wh/kg for a flywheel.