There had been rumors of a combined Chaos Gods codex now for some time, and the rumors had always pointed to Tzeentch being done first sometime next year, possibly June or July. This morning we have a bit that moves that timeline up, and answers some of the investigative questions regarding the Nurgle and Khorne leaks we have been seen.
Please remember that these are rumors. The previous leaks from 4chan can be read at the following link.
http://natfka.blogspot.com/2013/11/nurgle-codex-supplement-cover-seen.html#more
http://natfka.blogspot.com/2013/11/khorne-codex-supplement-with-cover-art.html
via an anonymous source from the Faeit 212 inbox.
very little plans have been made for khorne or nurgle supplements and they are unlikely to include large model waves. Tzeentch will be the first of the supplements in feb but I doesnt know of any models to be released alongside.
Regarding the Nurgle Image leak
Also fyi, analysing the image file, this image was originally created on 25th july 2013 and then later modified in CS4 with an additional layer to add the 40k logo. Am trying to isolate the original image source