Originally Posted by
skywardhunter
Mass and balance. It'd be aerodynamically inefficient and a safety hazard.
What are you talking about? The shift of 18" doesn't cause much, if any change in balance due to the weight being close to the CG. Otherwise popular aircraft like the MD80 wouldn't fly due to the 2-3 seating.
In addition, there's no more safety hazard than a 3-4-3 setup