I, too, would like to have charging at Superchargers, but more practical for all of us would be a liquid cooled PEM, or improved brakes. But my guess is that it will be something else, and probably something relatively inexpensive for both Tesla and owners... such as converting the Roadster to keyless ignition, possibly with a fob that shows some data such as SOC, charging status, maybe a locator function for parking lots (when every other car is hiding the Roadster!) Of course, there would have to be an accompanying (vast) betterment of fob range... Or maybe it's something we haven't even guessed at; Elon is a pretty creative guy.