The Antonov 225 is the largest cargo plane in the world. But how much bigger could you REALISTICALLY make it if money wasn't a problem? Could it be say twice as wide? Carry twice the weight?
What materials and physics constraints are engineers up against? Is there a limit on today's materials to make a larger cargo hold or wings that could stand the bending moments of more engines and fuel in the wings? Would runways not be able to stand any extra weight than the 225 can already carry?