What we need is useable area, not just a large total volume. I understand the greatest current problem woud be to design a feasible pressure vessel in any other shape.
The vast majority of cost savings over the previous 40 years has come from the engine design NOT the aerodynamics, why don't the chaps at Boeing and Airbus keep up with the amazing progress of the engine manufacturers. Or even try!
Isn't the A380 an oblong section?