The current release themes in the rumor mill have us seeing Tau in September... quite possibly the later end of it, but soon nonetheless. There are also rumors of a Chaos making an appearance, but Tau seem to be on the forefront of the rumors right now. Of these we have had some reliable information that there will be two new suits and a new commander.
Please remember that these are rumors.
via Darnok on Warseer
Tau in September should be about right. There are a few more AoS releases coming, but I don't think they will stretch into October.
via Bird in the Trees on Bols
Tau Empire Release
A “big” release (unknown if related to Tau Empire, but could be)
Codex Tau Empire
Tau Empire Datacards
Tau Empire Painting Guide
New Plastic Battlesuit Commander (in a new size of package)
via Sad Panda on Dakka
Age of Sigmar launch is still three full months in total. No shortcuts.
Tau are next, yes.
Campaign books or Codex first? I don't know.