The Chaos Grand Alliance Battletome is looking like it will be followed with additional Alliances coming soon. Expect the Order, Death, and Destruction to soon follow. Check out the latest Age of Sigmar happenings.
Grand Alliances are now listed on the GW Webstore
-Order Grand Alliance
-Chaos Grand Alliance
-Death Grand Alliance
-Destruction Grand Alliance
via Darnok on Warseer
There will be similar books for the other alliances. New Realm Gate Wars book(s) too. I have no information on the timing, except for "soonish".
Expect some WoC repacks soon as well.