This is a a very sad direction to see GW go with their products, recently my gaming group and I have starting playing 5th ed fantasy.
The reason I bring this up is that back then before they split chaos into so many factions you could get this 1 box simply called chaos. IT HAD EVERYTHING rules for all minis, all the cards you needed a complete bundle it felt like a real bargin as opposed to this supplement DLC model. Thing is I am sure GW make decent profits over that box, what matter is that we did not feel screwed over by it.
Any how back to dark eldar, if they bring out Vect say and Malys as a white dwarf rules I could handle that the price is not the same as the codex ( $83, I have to pay Australia tax), however if its a supplement they are definitely creating the feeling of being ripped off.