"The reason is simple. Any time a gap exists (and it must to allow the gun to open), every time the gun is fired, the two parts are "pulled apart" striking each other. Even if the gap is tiny, that will still happen."
Every time someone brings up top break handguns, this "gap" thing gets the blame. That's not the issue, as pressure is pressure, and if the contact stresses are kept low enough, no deformation occurs. The problem is the top break design itself, which puts the fram pivot far below the barrel axis, forcing a nearly insurmountable bending moment into the top strap and latch. If the pivot is even a fraction of an inch closer to the bore, these forces fall accordingly.
If you put the break joint in line with the bore, you don't even need a top strap. As far as latch gap or looseness, the trick is to use a tensioning latch, like a break open shotgun. Once tensioned, static friction in a properly designed latch will keep it closed. Wear will occur and the latch will eventually run out of tension, just like break open long guns, but it is a slow process with quality parts (and a good design would be serviceable)
I have something on the drawing board, but it is a large Rube Goldberg hogleg, just like the original break top revolvers, and I have other projects I want to pursue first (ones that are far cheaper tha this would be). I do have a Ruger 44 and 357 mag cylinder & parts allocated, though.
TCB