This caught my eye, and since I have no other information on it, it could just be speculation. However, the idea of Sisters being wrapped up into an Imperial Agents codex is interesting, especially holding Custodes and Inquisition as well. Also a Traitors Legion codex mentioned for December likely will determine rather quickly if this is speculation or has some traction.
Please remember that we have not heard anything else on this yet. Salt required. We will be keeping our eyes and ears open on this one.
via SharpDeadFace on Faeit 212
Sisters are to be rolled into an imperial agents codex due for release late this year / early 2017. They'll be with SoS, Custodes, Inquisition and most likely Assassins
Also there's a Traitor Legions codex due in December as well