Dwarfhoplite, maybe, with each player being randomly allotted dwarfs or choosing them, or say having a variant where you play as a telepathic guild leader rather then a force controlling the entire fortress. MrWillsauce, multiplayer adventure mode would be rather easier and much more interesting in my mind. The problem is getting the world to sync up according to the actions of the adventurers and each others effects ripple through the world, though group adventuring would be first most likely, and i would envision it happening on private servers. The easiest way would be time delays, but then again when you run into different playtimes and sleep in-game, you'd have some nasty messes, unless you made sure everyone had to wait for everyone else to catch up to them when they slept etc. Then again, theres the option of having time pass at a fixed rate, but considering it is a turn based game that would be rather tricky especially if everyone didn't know what they were doing. In summary; something which could be done, but if by toady, much, much later, and either through him or mods if they have the necessary framework rather difficult to do. The best way i can see it operating is with a group of friends. This has probably all been said before, so no need to carry on endlessly.
A sticky of discussed incessantly is an excellent idea.