Just sharing a concept I've been toying with that I'm considering trying to develop into a full setting, hoping to get some feedback.
Some time ago, two distinct, seperate Prime planes ended up actually colliding and, to a degree, fusing into each other. The problem that prevented a complete fusion is that one plane was ildly aligned with the forces of law, while the other was aligned with chaos. The regions that fully merged is of no alignment, much like most common Primes, but there are two regions which resist the fusion, in large part due to the influence of the gods of the two seperate planes.
The gods are, with one exception, not "true" deities. That is, they can do most divine actions, including resahping their personal realms, but they're wholly a part of the plane itself, much like the mortals are. They're essentially a step past epic-level PCs, incredibly powerful but still restricted in that they can be killed, although unlike most deities they don't rely on their worshippers for power. The two pantheons carry auras of law or chaos, respectively, and these auras are what actually prevents the planar fusion from occuring completely. The only god who doesn't fall into these strictures is Lusan, the Creator and Destroyer, who actually is a proper god, capable of granting clerical spells and residing on a distinctly seperate plane. He was actually worshipped on both planes prior to the fusion; his alignment is true neutral, which caused the gods of law to regard him as a dangerous loose cannon who was unfortunately too powerful for them to challenge and oust, and the gods of chaos saw him as a boring stick in the mud who made to much out of being orderly. These days, he's regarded as an enemy by both factions, for a good reason, which I'll explain further down.
The boundaries of the fused plane have largely stabilized, with shimmering curtains of energy visibly denoting where they are; passing through them causes a mild resistance, as one is actually crossing a planar border. The area inside the sections still 'pure' still retains the appropriate alignment traits, while the region in the fused area is much like any other Prime plane, aside from the Maelstroms and the regions they've struck.
Maelstroms are spinoffs from the planar boundaries, usually spawned when something causes them to shift slightly. When the planes first collided, Maelstroms were things of horrific scope that wreaked havoc across all three regions of the plane. They come in two forms, each one attuned to one of the two alignments. All Maelstroms rewrite the planar structure they pass across, with the law-aligned storms serving to lock things in to some unknown pattern while the chaos-aligned ones randomly disrupt things. To this date, no one has ever witnessed the effects of the two kinds meeting each other, or if they have they didn't survive it.
Lusan is the enemy of the local pantheons for a simple reason: with them blocking the planar fusion, the world is a malformed, distorted plane, disrupting the flow of the multiverse in the area, unable to move in any directions as the opposed 'bulbs' shove at each other, countering their motion and acting as a planar dam. Lusan, as the only entity with reach on the plane, wishes to remove this obstacle, and the most effecient way to do so is by exterminating one or both pantheons, or at least weakening them to the point that the plane can finally finish fusing and get about being part of the multiverse proper again.
The current era has things settled into more-or-less a Cold War state of things; the gods of law are loathe to leave their epicenter of power and expose themselves to increased danger, both from the gods of chaos and from Lusan's servants, and the gods of chaos don't want to leave their abodes for much the same reason. The neutral zone is finally developing nations as the scars from the original wars fade away, and those people just wish they didn't have to worry about an army overruning their crops or a Maelstrom transforming their homes and them out of nowhere.
There's more, but that's the overall gist. Opinions, anyone?