So I was throwing myself back into hell again (starting to replay the Watcher), minding my own business, when I suddenly had a flashback to that one lore pearl from Subterranean (it’s the teal one, I think), and went “wait… wait a second.”
“If you leave a stone on the ground, and come back some time later, it’s covered in dust. This happens everywhere, and over several lifetimes of creatures such as you, the ground slowly builds upwards.”
Implying the dust falls from the sky, since the Void Sea is what lies below, right? So… if it’s falling from above, somewhere…
(Endgame region spoilers below the cut)
There are falling stars in Outer Rim. The sandstorms here have the same green as the stars in it. There are things in the background apparently called STARCATCHERS. The architecture here is OLD. It’s Depths architecture, the same civilization that predated the Benefactors/Ancients/whatever you want to call the iterators’ creators by who knows how long, and it’s being buried in the sands by the ever-blowing sandstorms.
I looked at Shattered Terrace next since it’s the other ending-related endgame area and…
It’s newer architecture, more akin to the architecture we see in the base game, but it’s falling apart. Bits of rubble are floating off in defiance of gravity, while other parts of it have collapsed and been worn down into the dust you see blowing on the wind.
In Outer Rim, we see the ground being built up with stardust. In Shattered Terrace, we see the world dissolving. The two endgame areas of the Watcher are representations of the beginning and end of that very cycle of the world that Moon explains to us with the Subterranean pearl.