Just to add onto this idea of player made dungeon type things. Imagine if Necromancers could create zombies that you could stick in your keep during a campaign to be cannon fodder for people attacking your base when your guild is out scouting or something or maybe be a buffer between you and the rest of your team while you prepare for the attack in the deepest catacombs of your base. You could make it so that the necromancer would have to be within a certain distance of the zombies to keep them active and he could be like an early warning system for an imminent attack.
Of course if they end up spawning a lot of zombies in their base it might be annoying to have to deal with all of them so what if you send in your stealthy character to sneak past all the traps and zombies and such of said keep, kill the necromancer and then all the zombies fall dead!
Now all the attackers have to worry about would be other sorts of traps they might have set up. This type of thing would probably take a lot of work but just a post launch idea suggestion.