Thanks for the reply! Some interesting ideas!
My take:
Hawks: I can say with confidence that Hawks make no difference to me whatsoever. Bomb away. Played against them plenty of times and it has yet to make a substantive difference to a game.
Dreadnaughts/Wraithknights: Actually, getting these stuck-in with a pack of Bloodletters is actually *my* solution to *them*. Much easier than killing them with a Bloodthirster and a good way to give a pack of cheap infantry something to do all game.
As for the scary gas and the Farseers and the de-buffing invul saves--all good plans, and they would kill a bunch of bloodletters. The problem, though, isn't killing bloodletters, it is killing *more* bloodletters than kill *you,* and that's the problem. I think that's the central issue of tackling this list, honestly. My bloodletters are able to soak a huge quantity of casualties before it starts to matter. The fancy tricks that kill a unit at a time (like most of the stuff you mentioned) depend both on luck AND only really tackle units individually. So, unless you kit out your force with exclusively those things, you can't really address the army as a whole.
And that's even before we realize that you're kitting your army to kill 700 points of infantry in a 1750 point list. Pre-7th Ed, when only 'letters scored, that was a clever tactic. Now, it doesn't really help, and the other weapons I bring still work.
As for Maelstrom, that's a good point--I don't usually play maelstrom (the games are really random and this annoys most of us in our group). Of course, the thing with maelstrom is that, as much as I *might* be forced into a situation where it would hurt me, I am almost equally likely to find myself in a situation where I'm earning VPs ass-over-teakettle without even trying.
Hence why Maelstrom isn't too popular around here.
Final note: Certain Eldar units (Wyches, Dire Avengers, Storm Guardians) count among the few units in the game that give the Bloodletters pause. The combination of cheap cost, high Initiative, and many attacks make bloodletter assaults inefficient. Doesn't help you with Daemonettes, of course (and, seriously, the Slaanesh wave is WAAAY worse than the Khornate one).
I think it's pretty clear that, if one tailors a list to kill this, it can be done. All-comers or even tourney-metagame-lists are going to struggle, though, since this list does all the things that most lists
don't.
I've been trying to figure out an all-comers list myself that would work reliably, and it's really tough. And this list of mine includes a grand total of one gun (ONE!). People say "assault is dead", but for the Daemons is certainly is not.