I think it's less about the inherent structural integrity of the design so much as it is top break revolvers having no particular benefits over those with a swing out cylinder as well as the fact that few manufacturers are setup to produce such revolvers, and therefore there would be a number of expenses involved from R&D to tooling, so there's really no reason for anyone to design/manufacture a modern top-break revolver.

__________________
Shooting Comfort is bilateral.