Personally I think this is still a great time to be playing Chaos marine. While the codex might be "old", it's current simplicity gives us a great edge . I plan on playing as much as possible with my mech undivided lists, if only to be able to get a good grip on the rules changes and the effects it's gonna have on tactics ( for example, how the new mech rules changes how you deploy and use stuff. Flat-out-pop-smoke-first-turn to setup for a second turn rhino-shooty-rush anyone?) . And don't forget that the new allies rules opens up getting nice things like the amazing soul grinder.
After all, i really don't think there's gonna be that much changes to the basic chaos marines themselves, mostly point values, equipment selection and FOC_slot/cult_as_troops changes are the variations I'm mostly expecting ( Altho the possibility of losing true grit on the basic trooper does gives me a little pause). So then, why not just refresh yourself and your tactics, and then
see what kinds of new boosts we'll get with the new codex ? By the time the new codex hits, i expect i'll have the 6th ed tweaks down and then it's gonna be cake to integrate whatever new toys we'll get into the "crusade" (chaos-dragon-flyer thingie? Dreadclaw droppods at last? heavy stubber&autoguns cultists ?).
I'm also looking forward to trying out dakkapreds on the new rules amongs other things