I propose the addition of player-defined pockets of difficulty. These would be areas consisting of a 3D box defined by two points. Within them, the difficulty would be set to something other than the server standard.
Application
Each pocket would require 8 pieces of information: Name, Difficulty Setting, and two 3D coordinates. The pocket command would only be available to administrators/operators, and would have the following structure: /addpocket <name> <difficulty> [point 1] [point 2]. The points would be set either in terms of [<x> <y> <z>] or [<playername>]. If only one point was input, the player's foot location would be assumed as the other point.
Sample Usage
You want to make a floating island safe. You get your buddy Steve to fly high to the northwest, while you go low to the southeast. Command is then /addpocket peaceful Steve. The immediate area around the island is now Peaceful.
You have created an adventure dungeon in an external editor and would like to increase the difficulty of the boss room. To make a 100m cube, you input /addpocket hard 283 3 -1163 383 103 -1063 based on your knowledge of the room. (External editors would most likely have the ability to do this within the program)
Names allow for easier management. In addition to /addpocket, a /listpockets command would be required, plus a /deletepocket. No two pockets would be allowed to overlap, or if they were then either higher or lower difficulty would have to take precedent. That itself could be controlled by a boolean in the server settings to allow easier nesting.
Effects
Crossing a difficulty boundary would act as though the switch was toggled normally. Monsters would despawn as they entered peaceful, and health would begin to regenerate. If a mob spawned in Easy followed a player into Hard, it would hit harder accordingly.
Uses
Safe areas, from continents to closets and everything in between. Spawning areas, L4D-style saferooms, hospitals, etc.
Areas for monster combat on otherwise peaceful maps
Really, the possibilities are endless.
Downsides
This will almost certainly require an architecture change beyond what a mod would be able to provide. I am not a gaming programmer, so I am unaware of the issues involved in maintaining multiple difficulties on the same map.
After thinking about it some more, it seems like the easiest way to implement this sort of thing would be to put the points in an independent .config file. Not only would it be exceptionally easy to edit outside the game, but it wouldn't require any changes to the save file system.
Clearly I should have worked something at all objectionable into my proposal, since it seems that the only ideas that get attention are the ones that a portion of the userbase disagree with. Okay: you can set areas to hardcore, but when somebody dies in them, the entire pocket is wiped!
Sounded a bit confusing at first but what I am getting is that this is a thing for map makers. You can set the difficulty of an area to hard like a boss room then a area where you don't want mob spawning to peaceful. It actually sounds great for map makers but myself am not a map maker. But a good topic.
A rather good idea, if extremely hard to implement. This will probably just be one of those things that makes a nice pipe-dream but has no chance of being implemented. If it is put in I will be extremely suprised.
Sounds like something someone will eventually add as a Bukkit plugin hoenstly.
Application
Sample Usage
Effects
Uses
This will almost certainly require an architecture change beyond what a mod would be able to provide. I am not a gaming programmer, so I am unaware of the issues involved in maintaining multiple difficulties on the same map.
Conclusion
Clearly I should have worked something at all objectionable into my proposal, since it seems that the only ideas that get attention are the ones that a portion of the userbase disagree with. Okay: you can set areas to hardcore, but when somebody dies in them, the entire pocket is wiped!
Sounds like something someone will eventually add as a Bukkit plugin hoenstly.