Aka allowing for multiple people to use the same area without interacting with each other.
Why it is needed:
Take for example a dungeon. You have a group of 5 people going into this dungeon and another 5 about to go in. You don't want both groups inside because it would break both the mechanics and would clutter the area. So instead you instance it. Splitting the two groups of 5 into two of the same, but separate dungeon.
How to do this? [idea]
The idea is to copy the layout of a pre-built zone. Paste it into an open region that doesn't conflict with other areas. Then teleport the players to their corresponding dungeon.
players in group enter dungeon > plugin recognizes this > copies the dungeon from the template
> pastes template in open area > teleports players to the pasted dungeon > removes pasted dungeon when all players exit area.
If you've ever played WoW think of it like that.
I don't think this is even possible, but I have to think of a way to deal with dungeons and raids in some sort of manner that allows for multiple different groups to access it without interacting.
This is definitely possible (what isn't?). I would implement it by having a dimension specifically to run the instances on. As long as each instance is out of visual range of the others, there is no interference. If it's set up properly, you can just build the instance in mcedit or worldedit or whatever and paste the finished map in some folder or maybe import it from in game with a command.
What Vorquel said. Alternatively, one could make separate dimensions for each instance, which would eliminate the risk of sounds / player nameplates from one dungeon being audible / visible to people in a different instance of that dungeon if the two are physically nearby in the same dimension. However, that would be at the cost of performance; running an entire dimension per instance would be unnecessarily taxing.