Last ditch gamble for someone to survive? Whatever is on Arkhona is good enough to get the Daemon Primarchs attention, maybe it's got the power to bail them out. I could even see an interesting side story about Vect arguing with all the Dark Eldar houses of who gets bailed and who doesn't.
Meaner! Dark Eldar don't wage war like the other factions. They use portals and stealth tech to launch lightning raids to procure slaves, sensation, and stuff. The triple S that any piratical evil space elf needs.
Also this, as Kilrane said they raid rather then wage war, it'd be impractical for them to do so in their current state. Surely, so many soul-fires on Arkhona would attracted a Dark Eldar host.
Surely. So does that mean they would capture or attack territory in different ways? How could they be implemented into the game itself? Or would they just be the same general concept?
I'm sure they would want to establish territory somewhere on Arkhona, but if you wanted to be super faithful to the faction then they would have the capacity to stab at fronts they normally wouldn't be able to access. Say, they had the ability to hit a territory that was two zones away despite those zones being owned by other factions.
Dark Eldar do have the ability to take and hold places of interest. I mean they do have Titan-class walkers after all. They just don't entrench like the other races. I think that a powerful ability (borrowing a bit from Darthy) is not having to worry about supply lines.
The only other factions I'd have added are Necrons, Tau and Dark Eldar. But to be honest I don't really want any more factions added at all. I feel like it'd cause trouble with population balance and map flow.
Im just biding my time under the banner of the Black Legion till they put Death Guard in, then im jumping to them in a heartbeat. As for implementation, well its too early to tell, id have to wait till launch to see how much Gods will be given attention at first to know how id like the Death Guard to be. Id also like to see the Deamonhost take the scene as a faction or a subfaction of Chaos, and to go around as a Defiler ripping things to shreds with my claws.