One of the strong changes in the chaos codex is that challenges now must be accepted and given. Granted, there's very few challenges that my chaos space marines have been backing out of, but the inability to back out of them is now a cause for thinking about change.
One of the most used load-outs for squad characters (aspiring champions and the like) is the well tried- and well tested power fist. Sadly, the power fist will strike at Initiative=1. So, unless we're using plague marines with Toughness=5, feel no pain, or even Nurgle bikers of doom (and wow -- aren't bikers of Nurgle much improved in the new codex!) and the like, we need to think ahead about how to optimize this.
I think many players will be looking to power weapons (power mauls in particular?) as an alternative option for squad leaders. Striking at initiative seems to be important in these duals. If taken with the mark of Slaanesh, this means that against most armies, the champion will be going first and hoping to wipe out the opposition before they can get a move in.
Where is this all leading? Well, I think we're not only going to be seeing a resurgence of all types of chaos space marine armies, but I think Emperor's Children and Noise Marines in particular are going to be seeing a fair amount of play. If we couple striking first with lots of small units of Slaanesh marked marines, and the occasional re-roll on the dark apotheosis chart, I think there's going to be daemon princes of Slaanesh made on the battle fields of 40k with increasingly regularity.
On the flip-side, there are plenty of HQs and squad leaders we don't want to get in to challenges. Ahriman springs to mind -- he just isn't going to make it against many close combat orientated units (at least compared to Abbadon et al.!). And some of the HQs seem pretty much well aligned with shooting style armies: consider even a regular lord manning a quad gun behind an Aegis defence line and you get my drift...