I did think about including a flyer originally, the voidraven would probably make more sense since it's mono-tasked (and if you don't give it missiles, probably comes cheaper than the razorwing) My issue then though is that potentially you've still got two turns of your opponent's flyers being on the table and yours not.
If the opponent takes a flyer and it turns up early, depending on where it is, I've got up to 6 dark lances and 4 disintegrator cannons that can have a go at it, which should give it pause for thought at least. Flyers still aren't all that common at my gaming group yet, so I'm inclined to leave it for now. ADL is the most obvious 'on the table' option, but something about it just screams wrong to me when thinking about dark eldar sitting behind a static defence line.
The Hellions are there for two reasons really, Duke's combat drugs extra roll, it seemed silly to have that available and not take advantage of it to boost the combat potential of the army (otherwise, there's just the one unit of wyches with combat drugs). I also like the fact that you get two poisoned shots each, plus hammer of wrath plus three S4 attacks each on the charge, and whe you add the ability to snatch independent characters from their support to let you wail on them alone in later rounds they just make me warm and fuzzy inside. They actually strike me as being probably the best all rounder we've got in the army, though I accept they're not for taking on terminators.