Howdy
You are not going to see a Top Break revolver produced in any high pressure cartridges like the 357 Mag. Probably the most powerful Top Break ever was the Webley, firing the various 455 Webley cartridges. A large, low velocity bullet, weighing around 265 grains and moving 600 to 700 fps. It was an effective manstopper, but it only developed about 13,000 psi, which puts it on a par with 45 Colt at about 14,000 psi, if memory serves.
The Webley was a big, massive gun. The latching system of the Webley was massive, compared for instance to the Schofield latching system. A friend cannibalized some Webley parts and installed them on a ASM Schofield, the ones that were notorious for coming unlatched.
But we are talking 35,000 psi for 357 Mag. You just are not going to see a Top Break chambered for that. You will notice that all of the current Top Breaks manufactured in Italy are chambered for relatively low pressure cartridges like 45 Colt, 44-40, and 44 Russian, and 38 Special. That is about all a Top Break is capable of, even with modern steels. There is a reason that all the revolver companies stopped making Top Breaks and started making solid frame revolvers at the turn of the Century. A solid frame revolver is simply stronger.
Regarding shotguns, yes, O/U shotguns pivot open, but the design is nothing like a Top Break revolver. Plus a shotgun is a much more massive mechanism, and shot gun pressures are relatively low, in the vicinity of 10,000 - 12,000 psi.
++1! The reason side opening revolvers still rule the roost is because they are so good. Developed over 100 years ago and still going strong.