Now, all they need to do is make the horizontal plane wider, add rudder and ailerons and propeller and they are good to fly (without wasting all that energy to overcome roll friction)!
http://en.wikipedia.org/wiki/Lift-induced_drag#Reducing_indu...
Currently they have this wing shaped in such a way as to keep it from flying off the road anyway, and this inevitably creates rolling friction. But why should they waste energy on this?
It's true that you could reduce your rolling resistance by making a car with positive aerodynamic lift, but doing so would make you dissipate more energy in the air than you would save.