This makes me think of Mage Vaults from a D&D playstream series I'm following, where they're left behind secred military labs from a long since fallen civilisation and they did some real crazy and unethical experiments there (not coincedentely the same channel also has a Fallout TTRPG series).
And given that Remnant used to be a basic fantasy setting full of magic, it's not hard to imagine that there might be places like magic Vaults.
Given that the Brothers genocided humanity in a temper tantrum in seconds, places like that might still be intact, and while they took most of the magic with them, it might not have effected the enchanted items left behind (or at least not as much as it did living things), as Dust is also magical and that's still around.
So if the main teams end up going Vault Hunting they might end up finding some crazy and incredible stuff (as well as all the unethical horrors done and recorded there).