Instanced zones is something I've brought up several times here in the past, and has always been met with curiosity, but no one really seems to have ever been curious enough to actually attempt it, and return with some kind of proof of concept. Personally, it might be something I pursue for Elysium. But that's a long way off.
Well, for the record I have a fully working instanced zone system up and running. Currently I only use it to create a deep copy of a normal area when a player buys a spaceship. It is different from the FotE solution in that each spaceship gets it own area, with its own private vnum range, and absolutely everything is copied.
I have also thought of other uses for it, like using instanced zones for assault courses in our military academy, and for certain types of quests.
This system was very easy to implement for me, because I had already changed how vnums work. In my system each area has its own private range, in that a "vnum" actually consists of two components. An zone ID + room/object/mobile ID. Thus all zones can have room 100, for example. So copying a zone is a simple matter of altering the zone part of the vnums. A fully qualified vnum is referred as <zone name/or ID>:<room ID>, like 4:100 or myarea:100. So I don't need to actually alter the IDs of the rooms within the zone.
This is one of the things that makes the FotE system a bit messy; it needs to find a suitable free "block" inside the area where it puts temporary rooms, and shift all the vnums. When the ship is deleted, so are these rooms. But this leaves that special area fragmented, and sooner or later you might end up in a situation where there is nowhere to put a large ship with, say, 50 rooms. In my case the instanced zone is a completely separate entity, and when it's no longer needed, the entire thing is simply deleted.
My approach makes many things very simple. There is no need to have any conditional code anywhere. The MUD simply doesn't need to know whether it's an instanced or a permanent zone.
If each zone didn't have its own private vnum range, though, this wouldn't have been as straight forward.