I like the idea pay attention to narrative potential of the Gatetowns, where the faction war isn't so limited and subtile like in Sigil.
* What if there is a second layer of the Outlands working like a rocky Dyson sphere, with a "planetarium"-shaped city in the middle, with secret portals toward the Radiant Citadel? And the mercanes creating floating islands where install their business premises. And a planar rift orbiting like a comet, giving sun light but not giving too much heat. There are some green zones, but also suspects of activities by defilers among the planar refugees from the Athasian Tablelands.