Up until now there rules where go if you where into uber armies but now 5th is coming out they will seriously need a re-write. I now of 4 Dark Edar players and all have uber armies with only 2 troop choices there stuffed now.
But the reason you don't see many Dark Eldar armies is that the minis are a tad dated now.
I march before a martryed world, an army for the fight
I speak of great heroic days of victory and might
I hold a banner drenched in blood
I urge you to be brave, I'll lead you to you destiny, I'll lead you to your grave
Your bones will build my palaces, your eyes will stud my crown
FOR I AM KHORNE THE GOD OF WAR AND I WILL CUT YOU DOWN