I won't call Scourges a bad unit, I'm sure a bunch of people will find some very good uses for them.
Maybe squads of 5-6 with a pair of haywire launchers. They will be mobile, able to do some damage to any target; ghostplate is one of the best armours for dark eldar, so it'll take an above-average effort to kill them (they'll be even tougher if they can take out a weak unit early, like a lone skimmer or IG platoon command squad; to get FNP).
However, if their problem was they had to compete for heavy slots; they haven't lost that issue. Now they compete for fast slots; and jetbikes and skyboards are looking to be all the rage right now.
To me, I see Scrouges in the same light I see Incubi... wait, before you all start booing me!
I love the background to both; but I think other things are able to fill their spots in the army, do a very similar job and in the end, be cheaper points-wise.
That's why I said I love bloodbrides so much in my first post.
A unit with a leader with agonizer, one with a shardnet and two with razor-flails is going to be awesome. That's 4 power weapon attacks that wound on a 4+, 6 attacks that re-roll to hit and to wound, then 21 basic attacks; the unit then has a 4++ save in melee against, and reduces the number of, enemy return attacks. This isn't counting getting a charge, or combat drugs, or the possibilities of pain tokens.
And it all comes in much cheaper then (almost half the price) of Incubi.
But in the end, I don't feel Incubi are a bad choice and I wouldn't tell people buying Incubi is a waste. I just like a different choice more.