I took this quote from the Brandonology site. Reading the above, I get the impression that some of the stories or rather, some of the worlds Brandon has already written about take place on a different plane of existence from each other (I.E some of the worlds could be in the physical and some of them could be in the spiritual).
Assuming on the right track, and given my crippling inability to proper express myself, I'll try and focus on my main points/questions instead of rambling:
Mistborn could possibly take place in physical realm (This is just supposition without supporting facts. You could replace physical with spiritual if you wanted I suppose, just not cognitive since apparently Shadesmar takes up all of that).
Elantris could possibly take place in the spiritual realm (Same as what's in parenthesis above).
Since Roshar is the first world where we are introduced to Shadesmar, is the current consensus that if we were to see maps of Shadesmar in other books, Shadesmar would form a mirror of the world/plane you access Shadesmar from? So if you try to access Shadesmar from the Physical plane, Shadesmar is a mirror of the physical plane and if you access it from the spiritual, it's a mirror of the spiritual plane?
Are the physical and spiritual planes able to interact without Shadesmar, or is Shadesmar required for either one to affect the other?
Assuming that the physical and spiritual planes can't interact with each other, but require Shadesmar as a intermediary, how likely is it that the shattering of the Shards of Adonalsium took place in Shadesmar? I haven't read the books that aren't canon that Mr. Sanderson have wrote, so I have no knowledge on this subject.
Lastly, do changes in the physical realm affect shadesmar with the same going for what happens in the spiritual? I'm under the impression that the Shadesmar can affect either one of them, but if the physical and spiritual can't directly interact with each other without Shadesmar, does this mean that changes which occur to Shadesmar as a result of one or the other don't transmit to the respective plane of existence?
I realize that a lot of the answers to my questions don't exist and that some of what I said is probably flat out wrong. If there are any theories on the subjects though, I would greatly be interested in reading them.