The latest batch of FAQs from Games Workshop haven't gone in favour of the chaos space marines, it seems.
For chaos space marines, the Warptime ability that is (was...) often interpreted as meaning one can re-roll failed to hit and to wound rolls as you choose has now been downgraded to re-rolling everything or nothing. In my opinion, this means the points cost just got a little too steep to be competitive (perhaps). So for my daemon princes of Nurgle, its back to doom bolt and Nurgle's Rot methinks.
Lash of Submission also suffers: a roll to hit is now required. That also reduces the points spent to benefit ratio.
Other changes in the FAQ are simply clarifications, mostly devoted to the character HQs and their weapons. No really surprises, but Kharn with a unit now prevents them from being affected by the Lash of Submission (for instance).
In common with the Daemons FAQ (for chaos spawn), the chaos marines FAQ now makes it clear that summoned daemons (e.g. greater daemons) that come on to the board where there isn't sufficient space still come on to the board and the other miniatures must make way.
Tzeentch's faithful rubric marines also suffer: without a sorcerer they may not be able to move if under the influence of a power that reduces the number of die they roll for movement.
Interestingly, Dreadnought fire frenzy line-of-sight arcs are now specified as 45 deg to the front of the walker. This makes the walker more tempting to take in regular armies for me.
Overall, some neutral changes, but mostly the FAQ reduces the points cost to benefit ratio for what originally was a sub-optimal codex. But to my Blood Ravens, Black Templar (etc.) friends: it's not going to help you :P