My understanding is that with the model S and X, the dual charger option means you can charge at 2x10 amps at 240V for 40 amps @ 240 V, but there's only one connector on the car. Wouldn't it be useful in many cases to have two connectors on the car? Some cases I can imagine where this would be useful are plugging into two street charging poles when no one is at two adjacent spaces, or plugging into two 240V wall plugs, or 2 120V plugs, or even one 240V 240V and one 120 V plug simultaneously. It would seem to me that having the option of choosing either two independent supplies via two independent plugs, or ganging both together to get a higher current through one would be a major advantage. The cost would just be the extra car plug and a relay in the car I'd think. Driving an EV in the wild is still a bit of an adventure, so the more options the better I'd think.