Okay, I know practically nothing about the universe but I've read that this is a game that appeals to Incels to the point where the discussion boards about the game double as Incel indoctrination sites. How much truth is there to that outside of what the "mainstream media" says?
I don't like the term Incel, it is very derogatory. It is true however that such hobbies do attract people with let's say lower social skills and appeal but they are still a minority and every hobby group has these.
I am a member of a gaming club that focuses on tabletop games, amongst them all the games that Games Workshop produces including 40K) and we have a broad range of people - young singles up to people closing in on retirement age with families. It is a very social hobby and i love our Friday gaming nights with all the trash talk, dice rolling and hobby talk.
Cavill loves the lore of Warhammer 40.000 and is very knowledgeable about its background, which fills me with confidence that at least he'll try to do it right and stick as close to the background as possible. He also has the acting and general film experience and let's be honest he's close to 40 so only has a few years left to play action heroes and it would not be unwise to lay down the tracks for a career behind the camera.
As to 40K there is enough material for all kinds of far future storytelling:
- current timeline with stories about Space Marines ( the main attraction of 40K, huge and genetically modified supersoldiers in power armor) fighting against various enemies from mindless animalistic aliens called the Tyranids, other alien races of heretics
- stories centered on human soldiers with occasional Space Marine cameos ( personal favorite would be stories centered on Gaunt's Ghosts, an elite imperial regiment whose home planet ws destroyed by Chaos forces and they are the first and only regiment)
- stories centered around the various inquisitorial forces working deep in the shadows trying to root out traitors, heretics or alien infiltration, much more small scale and would be ideally suited for a TV show due the scope
The big one though is the Horus Heresy, a massive civil war within the Empire of Mankind 10.000 years before the main timeline starts. During that era called 30K the Empire was expanding rapidly throughout the galaxy by military means, aliens were simply wiped out and old human colonies were given the option to join the Imperium under their terms or be conquered. For this reason the Emperor of Mankind, humanity's strongest psyker and leader of the entire race, has created 20 Space Marine Legions ( 2 were completely wiped from records without explanation, something fandom has been discussing for decades as to why

) each lead by a demigod leader called a Primarch.
The "best" Primarch called Horus was given complete military command in absence of the Emperor who returned to Earth to further other special projects but Horus was wounded and corrupted by Chaos forces ( evil gods from a different dimension called the Warp) and led half of the Space Marines legion and half of all other miltary forces in a civil war against the Emperor.
This massive event, written down in a 50+ novel series, has defined what 30K and 40K was and had repercussions all through the lore. I'm not sure if Amazon would be willing to do this properly as it would mean a huge investment of money and effort to do it right.
Best bet is they'll launch a few shows to build up the brand and then switch to movies to expand before launching into the Heresy, that's at least how i would plan this.
I guess over the next few months we'll get information bits here and there as production ramps up, writers, directos and showrunners are found and there is something to show. Right now it's the concept and planning stage but i envy Cavill for being able to do this with Amazon money in the back.
If done right it could have potential to rival Superhero movies.