We had a ton of other ideas (some of which, I didn't manage to write down, so those of you who did, please pick up where I leave off) we mentioned, but didn't have time to go into any detail about.
One of those is the role of the Shadow plane compared to the other transitive planes. In original planescape, this plane is not a fully transitive one (it was a demi-plane), so of course the bloods at the mimir thought up a third transitive plane, named the Ordial. Is the Shadow plane a real transitive plane, or might it actually connect to the entire multiverse, as a sort of dark mirror of reality itself? Will there be a lot more traffic on the transitive planes while Sigil is stabilizing? Can anyone say PTC caravans without their heart thumping really hard (also, good idea for the Outlands - after all, caravans are reliable and safe, even if they are slow...something that planars might really want after the FW)?
What are the modrons up to? Besides trying to build a new pathway (see other thread), shouldn't they be focusing on rebuilding their power base in Mechanus? What about those pesky formians and that nasty little layer that slid in a while back? Could they be secretly building a doomsday weapon to take care of the pest (think an actual "mechanus cannon"), and are they shutting down their borders while they do it? Do they plan to slide that annoying layer even further, down to Acheron? Do they need the help of mortals to revitalize themselves, now that they are diminished? Can modrons evolve? Wouldn't the Guvners be perfect candidates to help reestablish modron presence?
What's up with this new Yugoloth tower in Carceri? Do the three 'loth towers form a trinity of some sort that will set off a new plan (or perhaps, an extension of Squaring the Circle, from Hellbound)? What of the Maeldur et Karuvik - did the fiends get their teleporting powers back, somehow? Did they have to deal with the yugoloths, or did they barter similar powers from the Upper planes (after all, other solars might have similar abilities)?
So many questions...which ones will we focus on, and what direction should we take?
The Ordial was directly referenced as well in Guide to the Astral as a theoretical plane bridging the Inner and Outer Planes to allow the movement of godlike power and belief from the Outer to the Inner, and the movement of substance to produce petitioner bodies and other such things, from the Inner to the Outer.
The purpose of 'bridging' sets of planes to allow the movement of something is what a transitive plane is. Hence the Shadow (at least in my opinion and the way the PSCS has been treating it up till now) is... only sorta transitive - nothing distinctly *moves* though it from one place to another. The way I picture it, and the way I think that the PSCS portrays it as well is still as a pseudoplane but like a spider or an ocotpus - sneaking its stealthy little trendrils through and into everything - building itself on dark half-truth reflections and shadows cast by the other planes.