I own the book.
You heard it here first:
In 12-18 months, there will be a new set. Warhammer: The Vengeance of Nagash or Warhammer: Rise of the Welds or...
Then an accompanying hard cover book with rules for those gods and realms.
This book having only a few pages of rules and lots of room for fluff lends itself to that approach.
Probably off topic, but I just spoke to my local GW manager and he told me they are working on a huge project but he has no idea what it might be. Maybe something related to AoS?18 months is a stretch.
I'm guessing they'll roll out new campaign books in a month or two and in 8-12 month we'll get somehting like you proposed.