Curiosity not criticism - why did you go for that design rather than a Blended wing body with a much larger fuselage volume for the wingspan?
Weight is the limiting factor as much as size though, as mentioned, consideration to paved surfaces and undercarriage. Also wake turbulence for following aircraft... not all aircraft will be anywhere near as big, and something so big will limit approach/departure flow.
Also handling ability, something so big will have a massive turnaround time, not only will boarding/disembarking take forever unless airports utilise more aircraft doors, but also the time spent cleaning/prepping the cabin between pax.
It appears to make more sense for smaller more efficient aircraft, which is why 787/A350 seem to be the future rather than 747/A380