Minecraft Instancing Between Players.

It would be cool for other things to act like the Enderchest. Like expanding the inventory of the ender chest, and let's say player one is doing some.sort of custom missions and another player is playing that same mission but it's separate between the two players but in the same location. It would open up a whole new world of map making for people. I'm not a coder so I don't know how easy that would be but it would be awesome to have in game as some sort of function or command option.