I think you’re overlooking a somewhat botched advertising for Dredd. It wasn’t heavily promoted, nor made clear it was a reboot and not a latter day sequel to the Stallone one. It also somewhat suffered from its rating, being R in the US, and 18 in the UK, inherently limiting its audience at a time when most comic book adaptations were distinctly family friendly.

IMO the Eisenhorn/Inquisitor angle seems to make the most sense, as they could build a set of very human characters to view the world from, and include Space Marines as more of an ongoing / lurking threat (with plenty of scary action sequences to reinforce this), never having to stay with them, narriatively speaking. I mean it's rare for inquisitors to walk away unscathed (or breathing) from being sent to snoop around dark angels or space wolves, for example. So theres drama enough in that idea alone, let alone chaos or xenos threats

Astartes worked so well because the space marines were mute.

I would love to see a rogue trader based series, a rag tag band of misfits exploring an interesting but dangerous universe.

Or maybe I just want another season of Firefly.

tbh I feel like there's theoretically a shockingly good sit com set in the 40k universe.

I would add to the comments of the show being unapproachable, like Pariah Nexus, but I've shown Astartes to a lot of people and I've found that those 'questions' did not put people off at all. In fact they got very excited about the universe and came to ask me all about it. Those questions are hooks that get people invested in the characters and the world. Why does that Sister want to kill children? That makes her mysterious and intriguing. What is that mysterious man kneeling in front of the orb and why does he go insane? I don't think that unexplained questions are a bad thing as long as the show slowly trickles out answers. That's actually really good writing.

Interpersonal conflict: A Commissar and a Regimental commander who are both too well known for the other to think they can get away with shooting.
Fish out of water: Agriworld has to pay it's tithe so a bunch of farmhands get put through basic guard training and thrown into a centuries long stalemate conflict on a deathworld.
Space Marines: Henry Cavill has already answered that one "have them be cool from a distance" IE don't make them the main characters.

That's not a heavy bolter! That's an assault cannon!

Convinced the way to do a space marine thing is the same as Dredd tried to interpret the comics as "Dredd gets called in to sort a tower block, and then he does" like its plucked from a random weekly strip, do a skirmish like you're making a film from an actual game of 40k, and maybe make it Deathwatch so you can get multiple characters of different vibes interacting with conflicting with each other

Here's the solution: make a gotrek and felix series, but just for me

Honestly this pretty much reinforces my belief on why Eisenhorn: Xenos would be the best story to adapt:
Interpersonal conflict: Something I think you undersell to make out to be impossible and maybe is for the rank and file, but it's done very well in the Eisenhorn series, inquisitors and their retinue are given special privileges over the average imperial peon, you can actually have interpersonal conflict without someone having their head shattered by a bolter round a second later.
Fish out of water: That's basically what Bequin is, an average imperial woman who suddenly has a run in with an inquisitor, is discovered to have a power that makes her special and is taken from her everyday life on an adventure that takes her across the galaxy.
Space Marines: Xenos features two types, chaos space marines of the emperor's children and the elite deathwatch chapter, and the important part is they're used sparingly. I firmly believe seeing live action space marines is something that will keep people hooked and watching until it happens, so not blowing their load in the first few episodes to get people invested will be important. Cavill has already indicated he wants to use them carefully which is why I think we're more likely to get a "domestic imperium" centred story like Eisenhorn (who Cavill has also indicated in the past he would like to play) rather than starting an adaptation of the horus heresy.

You actually could do a SM show. But you'd need to make them Deathwatch as they have diverse attitudes, and they do have interpersonal conflict.

Bold of you to assume anyone at Amazon has either the ability or desire to make a good television show.

The upside of 40k is the richness of the lore. The difficulty is that it relies so heavily on trompe-l'œil style writing - words and descriptions which give an incredible sense of scale and atmosphere in the mind's eye, but being very difficult to actually put onto film. This has lead to most film depictions of 40k being extremely underwhelming and even the better ones feel like they are constantly struggling against their inability to depict the full scale of the scene.

Anyways, as for 40K being unadaptable? I disagree. But I will concede it’s a tricky adaptation. In a setting where the special forces are post human ubermensch armed with weapons of terror, you’re going to hit any certification board’s limit on gore pretty quickly. After all, Bolters and Chainswords don’t exactly do flesh wounds, and are favoured precisely because of that.

Yet leading with Marines would be a mistake, because they’re not the most interesting thing about 40K by a long shot. Instead, go macro. Zoom right in. Let us follow a newly adopted Inquisitorial Acolyte, recruited like Zemelda in the Cain novels from among the plebs, by simple expedient of being in the wrong place at the wrong time.

They then act as the audience proxy. The mere human finding out the terrors of the night aren’t only real, but more numerous than you could ever conceive. Keep piercing the veil, introducing ever harsher methods used to ultimately protect humanity from threats, including itself.

Be brave. Be bold. Sure give our proxy plot armour, but have friends and colleagues killed and replaced throughout, show us how they themselves eventually replace their Inquisitorial Master/Mistress in due course, having become a necessarily cold and heartless killer.

The series should be about a human bwing selected for training to join the Salamanders.
Struggles, growth, different scenarios, emotional capability, stakes.

The new Dredd movie failure can also be contributed to THE GIANT "3D" in there at time people were sick of 3D cinema. Because of it most people just thought in was another low budget cash grab. That is what I thought when it was released.

The thought about a docu series about the Badab war brought me so much joy, fuck that would be good

Fifteen Hours would make the PERFECT starting point for adaption.

It all depends on how it is adapted. A live action anthology series could work well. This way you get bite sized bits of 40k that are resolved by the end of the episode. Each episode could focus on different factions. Alternatively, make it more like AHS with each season being its own storyline. Rogue Trader would be perfect as it could follow a Rogue traders crew on their various adventures. The crew composition can be diverse perhaps with the odd xenos allowing for tension etc. It all comes down to what you choose to do with the material and which faction you choose to follow. There are things suited to a 20 minute episode in an hour long anthology and there are stories that will work as a single mini series or film.