Well, I refrained from giving any comments about this over at the Warvault, but I'll do it here.
The writing is nice enough. They have put some work in there, and the result is nice, and I'm sure it's a good piece of fluff. However, they just shouldn't have bothered with it. As I see it, there are two big problems with it:
1) It's not tied in with the NC campaign. At least at the moment, that is - they claim it will be, but even so, I can't see why they would have what is basically an entirely different campaign. Sure, a sub-plot is nice, and it's absolutely a good thing to come up with your own faction goals, like we did, and write about those. But this goes too far.
2) Second, it's not original. Sure, it's nice writing, as I already said, and the details may be a bit different. But in the end, the Chaos players are again having a storyline which basically says "stop us or you'll be destroyed". Big bad deamon, some clues, a leader with a horde of followers trying to summon the deamon, if he does the Empire will havyetothe foe in its lands. How original. Now, I'm not saying that it wouldn't be a nice story, after all, a lot of stories are built on simple concepts that are rather similar. But the NC campaign is already playing in the Empire, let these guys have their fun somewhere else - not every campaign/storyline has to play in the Empire and threaten it. I realise this totally denies the intention of the writers of this fluff, since they want to give Chaos a reason to be here except chasing the NC. But that's their problem.
This may come over a bit harsh, but I just think the Chaos players want too much. A sub-plot, fine; a totally different campaign, no. They'll just have to realise they're not the arch-enemy in, and the focus point of, every campaign.