[Big Dave]

One thing auto designers have found is that (except for sports cars) people simply prefer an upright seating position. It is comfortable, offers good visibility, and offers easy egress/digress.

Not everyone is an Olympic gymnast. Few people like doing a deep squat to get in or out of their car/truck.

Let's face it: The optimum low-drag shape for a car is a street luge. Think you could sell more than maybe a hundred?

Longer-term for very high MPG the "hedgehog" has to combine with the motorcycle and go to a tandem arrangement. Just slicing a Prius lengthwise won't do it as the fillet Prius would tend to flop over in a crosswind. A tandem will need a capability to lean into crosswinds.