You can look at a Smart car to see what a minimally viable passenger compartment looks like. VW made Beetles and buses with rear engines. A lot of modern cars don't have very big engine compartments, you need crumple zones, and aerodynamics are probably better with modern shapes, so yeah, I don't see cars looking all that different.

To your point, they're not even that different from stagecoaches--two people across, similar size.