Flying Car
The question is, will we use them? Depends on how far in the future you are looking. Sure, maybe after hundreds of years there will be flying cars, and poop. They could be more environment-friendly, and you don't have to fix roads all the time. But for now, we shall stick to cars.
Also, what happens when you have 50,000 of these up in the sky with no lanes or police of any sort, how would you pull someone over? Absolute chaos.