Warhammer Underworlds: Shadespire looks set for October, and they've also revealed the Ironjawz warband.
And they've revealed Malign Portents.
"Dark powers stir in the Mortal Realms. Malign Portents is a major event for Warhammer Age of Sigmar players, and it’s on the way in 2018. There will be big things coming both for the narrative of the setting and for matched play gamers."
I guess it's a summer campaign, along with probably a Death faction release