A bit out of left field, but rumors of Chaos Marines seem to come up every once in a while. I would say that as these rumors stand, this would be very disappointing, and the rumors are vague, showing little changes, and things being removed like Chaos Marks, but then again, this would follow the trend.
Please remember that these are rumors, and seem to be far out. I was not able to get much more information, even though I am trying. I am hoping to get more on this from the source.
via an anonymous source on Faeit 212
The Traitor Marines coming next Year:
-Few Changes in the Codex
-Undivided Mono-Lists only (no more Chaos Marks)
-Black Legion Suppliment revised