I’ve seen displays in aquariums that sort of mimic this - don’t have any pictures though.
IMO it wouldn’t be practical with piranhas. They are going to need all the space they can get and there’s a risk of jumping in a pauladarium. Also any of the terrestrial animals would be on the menu. If I was going to do a pauladarium I’d save it for something that utilizes the land portion or its prey does (African butterflyfish, archers, mudskippers, etc.)