GW is the most predectible company I have ever met.
We know that the next window is between October-November and, without Epic, they must release:
Space Marines
Cities of Sigmar
Warcry
Underworlds
Battleforces
December is a small month of releases and they sometimes releases Army boxes and Christmas content like Almanacs or gift packs.
I'm expecting one or two kits for Kurnothi of they are gonna be released during the next months. If you are expecting a medium or a big release then It must be released during March-April. The main problema of the Kurnothi is that we are waiting for content of at least 7 more factions and the size of the books is limited. You are expecting more content than Arks of Omen and Broken Realms together and that's impossible.