The 3 Realms remind me more of Doctrine and Covenants 131:7-8
LDS belief is that there are at least 2 layers to the universe: spiritual and physical/temporal. The scriptural quote above shows that they are really made of the same thing, but discerned separately to mortals. We do not yet have the "eyes" to see.
I'm interested in how this will play out in the cosmere. How close Realmatic existence is to this idea. Are the three realms really separate, or are they merely 3 ways of saying the same thing? Will any of our protagonists get to the place where they can observe/effect all 3 realms simultaneously?
Cognitive shadows are the body-less spirits of those that have died. Some stay, some pass Beyond.
Beyond seems to deviate from LDS thought as even heaven/hell is supposed to be a physical/spiritual place on the same plane of existence as us. Beyond seems to be a one-way door. You can enter, but there's not intermingling with the 3 Realms once you've gone in. It seems like his answer to The Last Question. Things don't just start over, they move on. Eternal progression.