The G1 Insight is somewhat close to that shape, though truncated. The rear wheels are significantly closer together than the fronts so the body can taper, and the body design really does work as is evidenced by some people exceeding 100mpg in it on the highway.
I've often thought it would've been neat had Honda extended the rear and made the space usable. It could almost certainly have been at least a 3 seater.
