In the coming months there's going to be another wave of unused/test/removed content related to the ingame maps - long story short, on top of there being test maps like pic related you can still load into in the game with the full set of assets, what sets Metaphor has "layout" files that basically define the whole list of things that have to get loaded when you enter a map, and there's some of these for maps that don't have all their assets remaining in the final build of the game.
I started digging into these a little bit recently because I'm at the point where I want to start spawning things on the existing maps that aren't there normally, but while that's going on someone else (same person working on the multiplayer mod) in the community is working on a tool for viewing navmeshes and other things that get called in these layout files.
If you don't know what a navmesh is, it's basically an asset-less version of a map used to determine collision, what the player can stand on, what they can't, etc. Navmeshes in games like Dark Souls are a huge pain in the ass to edit but they're often a treasure trove of unused content if you can actually get them open because they visualize map layouts in a way that you normally can't if the devs scrubbed any old assets from the build.
Should be cool stuff.