The idea is this: Allow the community to build, decorate, and share detailed dungeon rooms with each other, that are then linked together to spawn amazing underground dungeons.
A player places 2 blocks specifying the start and end of a dungeon room. 4 cobblestone walls and a ceiling are automatically created inside the points marked by these 2 blocks. The player then decorates the dungeon room, with the ability to replace even the wall blocks (maybe adding mossy cobble, or wool or wood for floors). The player also places special doorway blocks which specify where doorways could be placed. Then the player issues a command to save the dungeon room giving it a name. It is saved in a rooms folder. After a bunch of rooms have been created (the mod will come with a bunch of pre-built rooms), dungeons will automatically be spawned underground that consist of these custom designed dungeon rooms connected by stairways and corridors. Mob spawners from other mods are randomly placed in the rooms. The same goes for chests filled with loot.
The community will be able to decorate their own rooms and share their room files with each other. The header of the room file will contain a list of mods used to decorate the room. If the mods are not enabled for the current world, that room will not be used to generate dungeons for that world. There will be a config file for spawner blocks "modname.nodename" that will randomly be placed in the dungeons.
It may be possible to build sprawling interconnected villages and castles using the code from this mod.