[p1esk]

They will be autonomous, so no need to worry about parking: it drops you off on the roof, and flies away to a nearby charging station.

As for efficiency, yes, no simple solutions there. Note that they can still have fixed wings, the hover mode is only necessary for take off/landing.

[sokoloff]

My God. How did I miss that? Thank you for pointing out the blindingly obvious limitation in my thinking about cars vs autonomous cars. (This is a perfectly genuine response; zero sarcasm.)