Ah, gotcha. Yeah, there’s zero chance that you can make a pressurized pancake using rib-and-stringer architecture, probably even out of unobtanium. The best candidate I can think of is making it like a submarine, although that would definitely mess with the open concept floor plan and probably impose a huge weight penalty (although it might be helpful from a fatigue life standpoint). The only other remotely viable solution I can think of is drop stitching, but that has some fairly obvious drawbacks that would probably make it impracticable.

>pressure vessels as cylinders for even distribution of of the pressure forces across it. Ideally you want to have it capped off with two hemispheres

The pressures may be equal, but the stress (what I assume you mean by pressure forces) is what matters. The hoop stress is double the longitudinal stress (which is why pressure vessels almost always tend to fail by splitting along the longitudinal axis, despite both the longitudinal and radial axis' experiencing the same pressure). That would make me think the stress at the ends isn't as much of an issue, but I guess funky designs can act as stress concentrations.