It's clearly going to be Ogres and Bonereapers together first, as Ogres were first confirmed to be in a 'Feast of Bones' thing and then Ossiarch were revealed to be collecting the 'Tithe of Bones', so it's clear that these are going to be both released in a Battlebox that features the new Tyrant and existing Ogre models against a portion of the Ossiarch army, alongside the updated Ogre Battletome and all the other Ossiarch minis. This will most likely take up all of October.
Then GW confirmed that they were going to release those ghastly plastic Sisters of Battle in November, and knowing how GW love their Imperium stuff, this will probably take up all 4 weeks in that month, or if not, the remaining weeks will be taken up by Storm-of-Magic-for-40K.
Historically December has always been the month where GW just release a bunch of new SC boxes and Battleforce boxes along with other Christmas bundles, so I wouldn't expect anything here.
HOWEVER, January has always been an AoS month. This year it was Gloomspite Gitz, last year it was Maggotkin, the year before I think it was Disciples of Tzeentch and the year before that I think it was Seraphon (which was just after AoS came out in July 2015). This means I'm pretty certain the next AoS release will be then, but I'm pretty sure that it won't be Slaves to Darkness or Seraphon 2nd Edition.
I'm surprised that none of you have noticed that GW have already teased another new faction - remember the Kurnothi warband in Beastsgrave? GW have provided some physical evidence that an army based around these chaps is going to arrive soon, and the earliest they can arrive is January, for the reasons above. I'm pretty sure that Slaves to Darkness and Seraphon will be later on next year, probably in the spring.
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