Back in 3.5, I created my own setting, and jotted down a short history of the world, including a creation myth.
Now, I realize that many of the themes I used are deeply tied to 3.5 game mechanics.
I'd like to "tweak" my fluff to make it more 4E friendly, or even better completely not tied to any particular edition (you never know when 5E might kick in 
)
Chapter One "1st Era - The Age of the Divine - Celestials vs Fiends"
Heaven and Hell battle for dominance. From this war, the World (Tyrrah) is born. The great power of the Outsiders generates a Cataclysmic event that shuts down the connection with Heaven and Hell. The essence of Hell is sent deep underground, creating the Underdark.
The essence of Heaven is shot to the sky, eventually falling as rain on the worlds, creating great seas.
The combined power of the Outsiders, mixed with the very earth of the world, generates the Dragons.
Cut off from their Divine Realms, Celestial and Fiends gradually degenerate into Aasimars and Tieflings, humanoid races blessed with Heavenly or Hellish powers.
The greatest of the Immortal Outsiders linger and rule their race.
Celestials retire in a Oasis kingdom deep in the south, while Fiends rule the coldest reaches of the north.
So...with your general creation myth...
-Devil's don't -have- to exist in the astral sea...or rather, the astral sea doesn't have to be all "above the world". The pits of hell could be like an infernal aquafer of the astral sea, which sits below the earthy bit of your world.
-You can still have tieflings and devas as mortal incarnations of the celestial and fiendish servants, long removed from their divine/infernal parentage.
-The war between the Celestial and Fiendish could have happened -after- the 'dawn wars' where th immortals battled it out with the primordials. Asmodeus, seeing the gods weakend by the war, arose in fiendish rebellion. The split between demons and devils could also be another schism between devils...basically, the really, really rebellious fiends wouldn't abide the hirearchy of hell, and were cast into the abyss.
-The elemental chaos could also be raw firmament...the stuff of creation...no primordials needed.
Some other ideas:
-The wizard versus sorcerror idea which 3e mechanics capture well could be found again in a conflict between power sources...basically you could do Arcane versus Primal. The will of mortal creatures over natural spirits/magicks resulting in the arcane, and the primal attempting to keep the world it's own...where nature spirits, and genius loci rule their own dominions.
-Or, Wyrmlord magic could be a lost kind of power source/magic. It may have been a cross between primal/elemental, but the fey wizards destroyed the knowledge of it when they defeated the wyrmlords (or did they?)
-Angels and Devils don't necessarily have to be automatic enemies, but it can make sense if they are. Angels are servitors of the Gods, both good and evil, and they will likely not be fond of Devils (and possibly demons if you use the demon as variant of devil notion) due to the trouble the devils caused at the birth of the world.
Just some notions to kick around...hopefully some of them will be useful to you.
Indeed, once I set my creation myth AFTER the Dawn War, it all makes more sense. Basically, after the Gods and Primordials have sort it out among themselves somewhere in the Cosmos, my "heaven and hell" (and his inhabitants) have forged the World of Tyrrah.
Also, I'll change all references to Elves into Eladrin, since they're te magicky ones.
I'll tweak the History a bit based on this.
thx again
I was a little scattered brained yesterday...so I was worried that i wasn't making much sense.
Glad you found 'em useful!
Cheers