A few things come to mind (other than the near-impossibility of a start up pulling off a project like this):
- Is there a weight penalty to be paid to deal with pressurization in a flat body like this, compared to a cylinder or near-cylinder? How does this extra weight impact the efficiency?
- What does cabin evacuation look like for a super-wide body like this? Will there have to be be a larger number of exit doors? How does that affect weight and structure?
- At first glance, it would seem like the engine intakes are in a low pressure area. How does that affect efficiency? Maybe they are high enough above the fuselage that it is not a big factor but it seems like airflow management into the engines is going to be tricky.