Mercule
Adventurer
I can get behind this. For the PCs to be Important (capital 'I'), this is a necessary point. Not every campaign needs to shake the pillars of reality, but the Prime should be an anchor, when it does.All of the fiction is clear on this point -- you might have the occasional scene set in a god's court in the Seven Heavens or Nine Hells or some such, but the Prime is where everyone is /striving/, god and man alike. It's where all the big decisions are made.
I could get behind this. Maybe an island in the astral, rather than Concordant Opposition (or whatever). You wouldn't have to change Sigil much, just enough so that it isn't set, essentially, in the afterlife or the realm of the gods. Maybe have demi-planes shaped by refugees/agents of the outer planes, too. You'd end up with an astral version of Ravenloft, in a way, maybe even sponsored/controlled by an unknown(ish) force.If I had it to do over again, I would make what is commonly understood to be "Planescape" a sort of independent middle-distance planar setting, over the hill and across the dale from the wild and wooly "Manual of the Planes" portals and conduits that link the Prime Material to its gods' realms on the planes and back to itself. And then beyond Planescape you'd find ever more increasingly bizarre and unapproachable interpretations of philosophy and its effects on your surroundings, as the Prime Material worlds connected to those distant lands become more and more different from what you know and understand. Because if you allow for a certain distance across which weirdness from other realities can propagate, you can see how Planescape /derives/ from the multiverse so long as it does not interact directly with the multiverse.
If you wanted to make it even more accessible, you could let the demi-planes be something akin to a Purgatory, where souls are still able to be recalled by Raise Dead and the like (True Resurrection goes all the way to the Wheel). Since the true lords of the planes wouldn't be in residence, lower (mid) level adventurers could actually have some outer planar excitement without being insane. Since they'd technically still be in the astral, their souls would go to their normal destination, instead of being trapped. They'd also be subject to some much less disturbing natural laws, even if each demi-plane reflected its origin. But... adventurers would have to be careful because each demi-plane would have off-ramps to its origin, which could get nasty very quickly.
Done that way, Planescape becomes just another setting without breaking the shared Wheel. Still probably not my cup-o-tea, but I wouldn't grit my teeth whenever it's mentioned.