I got a closer look at warbands and saw that some of them have interesting backgrounds that do not show anywhere else in the game.
Goblin Gang:
See that goblin’s house with yellow light in it? You won’t meet it in known kingdoms nor factions.
Vampiric Thirst:
Background looks much like Ghulvania or Dark Court, but you’ll never see that element there.
Armored Legion uses Hall of Guardians background, Fire and Fury - Broken Spire (possibly), Entangled Woods - Forest of Thorns.
Will we see some new art in the game soon?