Multiversal Cosmology

One of the gaming things that has been rattling around in my brain for a while is the idea of a "Multiversal Cosmology" that, somehow, will tie the various planes of existence together (ala AD&D) with all the other role-playing games that I own.

Yeah, not quite sure where to start...

I know that at the very least, the Primal Order (by WOTC) is going to play a large part in how things are laid out.  I also know that I would like to incorporate The Book of Immortals (by Mongoose Games) into the mix as well.  How much of Planescape (by TSR for 2nd Ed. AD&D) remains to be seen.

I believe, if memory serves, that the plane of Nirvana was changed to the steampunk-ish plane of Mechanus and I could see that being a possibility if I ascribe that to the Moorcockian view of Law VS. Chaos in which case I could see Nirvana's transformation into Mechanus being the result of a loss by Chaos on that plane to the side of Law.  Chaos (as evil and as terrible as it is) is, generally, more organic and life-affirming than Law which leads to science, sterility, coldness, etc.  The birth of the universe is in Chaos.  Its inevitable heat death is the final triumph of Law.

Working in Old Ones, Elder Gods, and whatnot should be interesting.