Must be a perception thing. One way isn't "long" in the sense that its only 300 miles. Its 'long' to drive SF to Las Vegas. Basically any drive over about 480 miles of freeway starts getting long.
That being said, the 'long trip' scenario is somewhat of red herring. If you regularly travel several hundred miles a day then an all electric car is probably unlikely to meet your vehicle requirements. If its an occasional (once a year) kind of thing then creative solutions might arise to address it.
Were the Tesla guys willing to put a high power plug in the back I could imagine a 'trailer' which held a generator and a gas tank and provided power all the way there.