Door entry would be tough in all but the classic. Most of us who can afford the toys don't want to have to do gymnastics to enter/exit their toys. One of the things I like about the Elio is that it uses standard door entry and no odd lifting-canopy or large step over. I suppose conservative engineers have to start somewhere and to make the vehicle practical, it has to be able to be entered by a person. If the goal was to build strictly for speed or efficience, the entrance can be wherever. I haven't seen a rear entry car yet though. I mean, why haven't we seen a van with no side doors and the way to exit is through the rear. You could avoid door handles, door seams, etc... Maybe a two seater where the two seats pivot inward to allow exit from the rear. You couldn't exactly back into a parking spot but it sure would make the A and B pillars an interesting engineering exercise.