Reading through this thread, I understand there are many NWN nostalgists, like myself.
I believe the NWN system (itself based on P&P) should be the inspiration:
1- prepare the game (design, draw, put-up NPCs, encounters, write dialogs, script if needed (this part should be user-friendly, which is a challenge))
2- play as DM, during multi-player: summon, change small part of the environment (and, NO, sorry, you don't change the maps at this time, nor do you design monsters or NPCs !), move a (invisible to players) DM avatar to plan encounters/traps/events changes ahead of time, control NPCs/monsters. An OOC chat system would be nice (allows the occasionnal AFAIK), like NWN's.
I think the system has to support the fact the DM is also a player. That means he's not gonna play every single NPCs/monster, except if he really wanted it this way ! Ideally, it should even be possible to spectate only, if all events are well done.
Last I recall, NWN fell a bit short in the DM arena, as the DM client was cumbersome hence some DM modders had created some magic wands (one for summoning, one for changing placeables etc ...) that would concentrate all DM's powers in the quick inventory, which would eliminate the need to go at length through menus to animate the game. I think this was an excellent idea.
Some quick ideas on top of my mind:
- quick jump to players' party button, for when you were busy somewhere changing en encounter, and want to move ASAP to the party
- quick access to player's stats, skills and inventory. Ability to change them.
- loot pools that would be randomised at open times: game would pick up one of the pool's item randomly.
- ability to save the state of the game and start again later at the same point. Not everyone has the ability to play 10 hours in a row, so I think this is important.
OK, I think this is all I can think of for now