Maybe it would lead to people living smaller, smaller homes, smaller cars, smaller waistlines, smaller commutes and smaller consumption.
don't forget smaller motorcycles. it does not take many cc's/hp to pull an adult down the interstate at 55 mph. basically you need a power curve like a tractor.
i'm looking for the link to the fuel economy challenge that used to be held. i had an article in one of my magazines a couple years back that talked about it and the man that started it built the first fairing (in effect). it was an interesting read.
** Edit **
I found Craig Vetter's Fuel Economy page. 470 miles per gallon