There are additional leaked images out now for this coming weekends White Dwarf. The interesting part though is next week's teaser, "Slaves to Darkness, the Balance of Power Shifts Once More". We are looking at more Chaos releases for the Age of Sigmar it appears in the following weeks.
The additional leaked images can be seen here
also they can be seen here at this link via aracersss
The new Chaos book though is now revealed to be
The Grand Alliance
Inside the Grand Alliance, there are according to White Dwarf, 21 factions inside the book, including the Slaves of Darkness. A Chaos Lord on a Manticore is one of those in that faction. All in all, 158 battlescrolls are in the Grand Alliance- Chaos soft cover book. $33