The general belief by people lately is that this looks like Hardmode Goblins, as the graphics and such are similar to the stuff that the goblin summoners do, which makes sense. If so, you can get this the first day of Hardmode which... eh, it isn't TOO bad, though I woulda preferred earlier. But hey. It'd be easy-peasy to make a bunch of them on one character and give them to new characters starting the game out.This is going to be crazy expensive right?
Its going To be so Late-game that their will be no use for it
You craft it.
Looking at the Vault itself, it appears to have similar aesthetics to granite furniture or shadow chests, so I am going to guess we craft it from those biomes in early game.Given the above quotes the most obvious source would be crafting it from Luminite bars/ore given that all "void" based items so far are crafted from Luminite.
I hope it is available sooner but knowing our luck it perhaps it will be from the boss perhaps with a rare crafting ingredient with your aforementioned drop chance.
At least it is a new inventory extension as you can never have enough of those.