The basic premise of the campaign, is that the end of the Dawn War fractured reality and the Primordials were slain, their essence used to forge the First World itself.  This cataclysmic event created four time-streams: the Summerlands, the Elemental Chaos, the Shadowfell, and the Mortal Realms, albeit altered by the events of the Cataclysm.

I'm using Order instead of Law, though they function identical for purposes of domains and channeled divinity powers.

The Astral Sea (Order)The Astral Sea exists outside of the time-streams.  It is home to the Gods and Goddesses and their servants, the Angels.  It is like a nebula of stars and silvery mist.

The Elemental Chaos (Chaos)
The Elemental Chaos is the most altered time-stream.  It has no defined shape like the other time-streams.  Instead, it is like a nebula within the triple-helix of the other three. Demon-Lords and Arch-Devils corrupted their time-stream and sundered the world, creating thousands of personal domains. They bound the essence of the slain primordials to their will to create the Archons, elemental soldiers to battle against the Angels of the Astral Sea.

The Summerlands (Good)
This time-stream is an eternal, primeval mirror of the Mortal Realms and is home to the Eladrin, an immortal race of feyfolk locked into a brutal war with the Shadar-Kai of the Shadowfell.  The Summerlands is anathema to the Shadar-Kai of the Shadowfell and their servants.  They are weakened upon arrival in the Summerlands and subjected to crippling pain that strips away their undeath, leaving the corpse to rot and return to earth and loam.

The Shadowfell (Evil)
The Shadowfell is the dark mirror of the Mortal Realms.  It is home to the undead race of shadow creatures called the Shadar-Kai, also called Shades by the commonfolk in the Mortal Realm.  This time-stream is anathema to the Eladrin, who have their immortality stripped from them if they travel within the Shadowfell and are weakened by the constant ebb and flow of necrotic energy until they succumb and their souls are wrested from their dying body and turned into wraiths and banshees.

The Mortal Realm (Balance)
The Mortal Realm is home to the dwarves, humans, halflings, elves, dragonborn, and other races.  It is the only time-stream that is not anathema to any of the others, thus making it the perfect battleground to shift the Balance towards one time-stream or the other.

Conflicts
The Eladrin and the Shadar-Kai each seek to dominate the Mortal Realm, believing it will shift the balance in their favor.  The Eladrin want to offer the people of the Mortal Realm everlasting youth and longevity tempered by vulnerability to death through injury.  The Shadar-Kai want to snuff out all life and raise them as undead servants.

There's also the brewing conflict between the Demons, Devils, and the Angels. Though they are often thought of as myth and legend in the mortal realm since neither has been seen in hundreds of years since the fall of Bael Turath.  The timestreams shift closer as the campaign progressess, creating natural portals between the worlds and eventually wholesale melding as parts of one timestream takes precedent over the others. The ultimate goal is either the unification of the time-streams or a stabilization of the current streams, which is up to the actions or inactions of the players and their characters.

Finally, one last wrinkle in everyone's plan is the possiblity of the ressurection of the Primordials and a revival of the conflicts of the Dawn War.

What do people think about...

Chronoweave: The Wake of Kronos

Also, what kind of temporal mechanics would you use / look for in a D&D 4e game with time travel?