Not an aeronautical engineer, but understand that the cylindrical shape used in today's aircraft design is very good at containing the stresses of a pressurised

Not an aeronautical engineer, but understand that the cylindrical shape used in today's aircraft design is very good at containing the stresses of a pressurised cabin. However, the design does mean significant pressure stress on the front and rear of the cylinder. This must be managed with extensive (heavy) structures. A doughnut design, in theory at least, solves for this by removing "the ends" of the cylinder.