It’s an ancient idea of @idonotlikeusernames’s from before Chapter 4 released based on the Father confrontation at the end of Chapter 3. Here, branch-cutting doesn’t mean something implemented that was removed, but rather a more wild theory not panning out to instead have a simpler but more reasonable solution.
Context (Quotes)
Updated thoughts on Sojourn are back to the Old Brauracha having built the City. This matches with M’kyar’s dating (“This place has been here since Braurach of old”), and still places it as a foil to Vigil: both Storm-source and Stormhaven (Vigil is the eye of the storm, and “Nothing from a Storm touches it, and nothing and no one moves in it—not that I’ve ever seen”; while the City shelters us and sends us back to the ‘civilised’ world, where the storms will follow; and Sojourn is becoming a beacon of rebellion against both Xaos and, given the upcoming firebombing campaign, Hegemony).
The heart of these “XoR post-apocalyptic” ideas, I think, is the parallel between the end of the world when the Hegemony falls to the legends of a wild age of wisards and monsters (and implicitly political fragmentation), which we find in the legends of the Knights of the Gryphon. Notably, the world a thousand years ago doesn’t actually need to have had its own apocalypse for that to stand. Since the beginning, the story can be read as a legend about the end of the world:
One day, the legend of your rebellion against the all-powerful Thaumatarch of the Karagond Hegemony will be retold in countless versions.
This is also the inverse of the Xaos-lands: the present day is the stuff of legends, full of magic and monsters and struggle, while a more stable and comparatively peaceful time is left to the nearly-forgotten histories. All of this is to pose questions to the reader about what their world will look like at the end of the road.