Looks like if you ever hit a pebble on the road it would probably flip and kill you. Note also the conspicuous absence of a seat belt. Cute little death machine.
It's easy to make a 100mpg car. All you need is to make it small, flimsy, no aircon, no heater, no stereo, no airbags, toss emissions standards out, pack you in like a snake going up a bear's anus, and drive around at a steady 25 mph without any stops.
I'm not sure I'd want to do 45 in that thing, hell of a way to go if you got speed wobbles. I could see a use for kei vehicles in downtown areas. Traffic is so bad that a car's top speed might be 30 if you are lucky. Mass transit, bikes and tiny vehicles are what most people could easily get away with day to day.
OK, but this appears to carry a maximum of two people and doesn't look like it has a trunk, so...how would this be better than public transit? Realistically, anyone who bought this would still need a full sized car to support a family of more than two, so this thing would only work for single people or childless couples. It's cool, and certainly better than everyone owning their own sedan, but not exactly a practical solution to car culture.