The big news is
Battle brother are
Eldar + Dark Eldar
Chaos Space Marines + Chaos Demons
All Imperial Forces
Armies Allied with their own Codex
Allies of convenience
Imperial and Eldar
Chaos Space Marines with Necrons or Orks
Tau and Eldar or Necrons
Tau and Space Marines are now desperate allies
distrusted allies has gone.
You can find the full table here. https://lh5.googleusercontent.com/-71myQ7gRwaM/U3vXkbzQEII/AAAAAAAAASM/WOA_ZRfas5E/s640/blogger-image-2122138276.jpg
7th Edition is going to be a lot more fun.