In response to the developer video, I thought it would be cool to have a network of underground "elders" from each race, gifted with immortality. These are NPCs whose quests are only available to faction members - possibly, the NPCs themselves have the ability to conceal their presence from non-faction players. These elders hold extensive experience and unique information regarding Molag Bal or the other Daedric princes due to many centuries of fighting to keep their influences at bay.

They can offer unique quests that help to provide a richer understanding of the Daedra and perhaps permit the faction members to attain unique weapons, armour, magic, etc. that can then be used in the general story line. Perhaps the developers could chain quests between several Elders, with a suitably monstrous huge reward for the player's dedication to the faction.

Upon joining the faction, the player is granted a unique spell that allows them to see the location of any nearby Elders on the world map.