Looking at the codex entry, we can say for sure that there won't be a chaos cultists kit as long as Dark Vengeance is on the shelves. Just like we haven't seen Killakoptas yet.
All the options in the codex represent exactly the cultist models from DV, so why should they release a seperate kit? It wouldn't add any new weapon options and only eat the sales of DV. The codex is clearly written with the knowledge in mind that there won't be any other cultist models (apart from DV) out for a long time. Chosen and the Helbrute might be different because there are a lot of weapon option yet uncovered.