Jasko:
Quite similar to the Kings of War writing competition, Black Library will start an open submisson window from end of August til end of September
https://www.warhammer-community.com/2019/08/14/your-chance-to-write-for-black-library/
Caveat for us is, that they’re limiting submissions to the current systems. On the other hand, the Legion of Azgorh is part of AoS. I am not sure how likely it is that they commission a story about them, but who knows.
And the responsible editor said this about a very similar question:
Q: How do you stand on using obscure troops or units which are no longer in circulationGet your quills, guys! Let’s make Warhammer Chaos Dwarf again. :hat
A: If they fit the story then it’s probably OK. We’re unlikely to commission a story purely based on it involving, say, necron Pariahs or Squats though!