The End Times second release wave is rumored to be right after Dark Eldar, and consist of several new models, a cult of Slaanesh for Dark Elves, new Chaos Lists, and more.
Please remember that these are rumors.
via Steve the Warboss on Faeit 212
The book includes, what I know;
-New Archaon Profile
-Cult of Slaanesh for Dark Elves with a new Unit and Chaos Demons
-Chaos Mono-List for Nurgle with Warriors and Demons united
-New Nurgle Chaos Champion (Valnir Aesling?)
-There is a picture with Nurgle Demons and a different looking great unclean one (I'm not sure, new model or convension)
-Some old Chaos Warrior Chars returns (van Horstmann, Arbaal, and the Tzeentch "make dead alive" guy)
THE FOLLOWING IS SPECULATION BY ME!
We may expect the following boxes:
-A special Slaanesh Unit for Dark Elves
-New Chaos Warriors / Chosen with Nurgle options
-Maybe new Unclean One
The book probably has three focuses:
-Dark Elves battle Khorne incursion in Naggaroth
-Nurgle incursion in Middenheim
-Archaons Chaos Army marching on