Some unrealistic ideas Just floating around in my head again:
Remember dungeon keeper? How about if players can take the roles of either the well known and respected heroes or on the other hand join the forces of Morgoth and oversee the minions of the pits ...
Changes and scope:
On character creation the players can chose to join the heroes or the forces of Morgoth with the task to defend the pits of Angband.
As Player they play completely normal, when making the other choice they would control a ghost-like creature which can spawn vaults, monsters, uniques etc -- against points. These points are accumulated by killing players, having players enter the current level. However changes to the level design - like a vault cannot be performed while heroes are on a level. Multiple DMs share points and receive only fractions. When doing any summoning action they have to follow all rules of minimum depths, so OOD monsters can only come via "vaults" (which brings also items to the levels...)
Furthermore they would have to have some specific powers to able to move around quickly - Base stats could be: spd +30, pass walls, float up/downwards, always see heroes, monster friend, see map, lite 0.
Beware that those DMs could also die - Once they would be in LOS or ESP range of a hero, most of the DM powers are lost (no more floating up / downwards, no summoning). On the other hand the DM would get some offensive capabilities and the ability to spawn an escort when being attacked. These strengths depend on his level. E.g. A level 1 DM might get only a weak magic bolt or even only blink away and some kobolds to defend him, while a level 50 Dm would be able to summon a demon escort (or the strongest the current depth allows) and some nether / chaos attacks abilities.
To avoid that DM and players play together secretly killing monsters / uniques / stuff that the DM spawned should cost him EXP. Maybe the level should also prevent (certain) monsters and uniques being able to be called.
So I dont want to make it too long to read :)