Even small changes to time tested designs provide significant risk. A completely new body style will inevitably provide completely new failure modes.

Pressurizing a tube vs pressurizing a pancake (or flattened sphere, or some other easy approximation) will have very different mechanical loading characteristics. Turbulence (differences in air speed/pressure) across a large flat-ish surface that also has a signifiant pressure differential will also prove challenging to design for and scale up.

Aerospace is a very high dimensional design process. Doing anything different puts you into unknown territory real fast.