This isn't really a request for one to be made, but it would be appreciated if someone did. If one has been made that does what I'm asking, it would be greatly appreciated if I was pointed in its direction. I'm looking for a plugin that is MultiInv-like in that it separates inventories by world, but allows inventories to be transferred between the overworld of a world and its corresponding Nether and End. I haven't found an option that allows this yet in MultiInv.
multiinv does this. in the Config, you have to create a group (Say we name it "Normal") then in the group, indented, you list every world you want in it Normal - Overworld - Overworld_nether - Overworld_the_end but with whatever your world names are of course.