I found some interesting stuff on ArtStation that shows some concept art:
https://www.artstation.com/artwork/Ve5XX
https://www.artstation.com/artwork/Ddwq0
https://www.artstation.com/artwork/llzYe
Also found this:
https://www.artstation.com/artwork/QddaZ
Not sure if this latter one has anything to do with the more recent game, but it looks pretty cool. Kind of has that “Warhammer 40k” look to it.