I think you're definitely onto something here, but creating a viable theory requires a little more understanding, I think, on some things that I have been struggling to come to terms with as well. One thing that seems pretty concrete to me, and which I feel is significant, is that the Old Hunters DLC really gets into establishing planes of reality. The moment where you pass through the Astral Clock to get to the Fishing Hamlet is a deeply symbolic moment. Yharnam exists beneath the sea of the Fishing Hamlet. Ludwig was tantalized by the lure Kosm sent down for him. Which is to say, the world of Bloodborne takes place at the bottom of the deep sea. Whats difficult, then, is figuring out where Dark Souls takes place relative to the deep sea. In Dark Souls, do you exist on the plane of Bloodborne's gods? or somewhere else entirely?