Yes, but that's like saying DnD setting like Dark Sun and Planescape were only made so Gygax could sell more books. It's technically correct, but that doesn't discount the quality or the ideas.
I don't think it is. Both of those were major projects designed first and foremost to be an RPG setting. I had to look up Pariah Nexus and from what I skimmed through it's a thing created to sell a mission deck thing for the table-top game. Very different emphasis. And again, the point is that nothing makes that specific location remotely required. You list off a bunch of reasons you want to use it which I'm about to come to, but you say that the complexity and size of the lore prevents you from doing WH40K. It doesn't, it would only prevent you using this one especially over-loaded (because trying to sell to all table-top players) location. So pick any of the myriad of others that you do feel capable of running. Though honestly, even in this location you've found I don't see it as a problem. So some people online are arguing over whether Sister's powers should work there? So what! If the setting says Sisters can, then they can. No in-universe character is going to be able to argue why they shouldn't and what does it matter if a player says so? Say you're going with the official background. What can be faulted in that? If this is such an utter problem that a player might disagree with the setting material just... don't have any Sisters of Battle with miraculous powers in the game. They're hardly an essential part.
Again, you do this thing where you first include something that you don't feel comfortable including, then say it's a problem because you included it. Nothing you have said in any of this is a problem with the lore. The lore is far more compartmentalised than the lore in any other setting that comes to mind. Because there is so much variation in different places and so little agency to freely travel between places. A WH40K campaign will only include what a GM feels like including. Far more so than Star Wars or any other franchise I can think of where there is more agency to go to different places and everything is close together in time that is in the default. WH40K spreads across ten-thousand years and a million worlds. Stop making life hard for yourself.
I must also add, it seems a little odd that GW would create a particular setting that has no psychic powers in it, as they're a common part of the setting. But whatever, it's one tiny part of the universe available to you.
Because, like Eberron, it's rife with gameable material.
So is everywhere else. If you want pre-made setting material there are whole sectors detailed in the various WH40K gamelines, none of which are the Pariah Nexus you seem fixed upon. And they are all rife with gameable material. The last thing any WH40K GM would normally want would be to try and include everything. Usually they have a specific area in mind. Rogue Traders, Astra Militarum, Inquisition acolytes, Underhive gangs... And you never run out of material in any of this. Pick one, I'll give you a list of things you could do enough for any campaign.
It's 40k, but it also has intrigue.
This is just absurd now. You need to use this specific area you have a problem with because "it also has intrigue". Where the Hell do you get "but it also has" about intrigue. The entire setting is rife with intrigue. Every WH40K game line, but especially the Dark Heresy ones, is full of intrigue. The setting drips with it. And you're talking as if this area is unusual because it has intrigue?
The plot takes place on a local scale, but has galactic implications.
It's WH40K almost everything is "on a local scale" if by that you mean a mere dozen planets or something. Let me look up this Pariah Nexus of yours properly.
Okay, so there's something like thirty systems here. So this is our calibration for "local scale". You have equivalent local scales (with more detail and NPCs and intrigue) than this in the Dark Heresy books and the more recent RPG. I don't get where you're coming from at all. You want "galactic implications". This is not hard to do. Make your campaign revolve around uncovering an Abominable Intelligence or find a complete Standard Template Construct or uncovering a Necron tomb world containing a C'Tan shard or the Emperor's personal journal or a lost Primarch or Greater Deamon. You're trying to justify a need to use this particular Table Top focused area just so that you can then say you're not able to because a player might dispute whether a small unit type of a single small faction should or should not work. And none of your justifications even make sense to me.
It allows for scenarios outside of hunting the chaos cult of the week.
You really have no clue what you're talking about. Go back to the campaign ideas I rattled off without even thinking and tell me that each of them restricts you to "hunting the Chaos cult of the week". This is why you're getting long posts from me dissecting all your points - it's because you're bullshitting and trying to blame it on something external that has nothing to do with it.
It's isolated, so PCs can do what they want want without wanting to fuck off to some other place that "matters" or simply call exterminatus.
So the advantage is that it's isolated and PCs can do what they want, but it has "galactic implications". That makes sense!
Anyway, This is WH40K. The place being isolated and PC's actions having no consequence is the single worst justification for requiring this area that you don't want to use yet. The Imperium literally loses worlds of billions of people through bureaucratic error. The core introduction to the setting back from 1st edition talks about how billions die every day in service the Emperor. If you want PCs to fuck around without screwing up the setting, that's the default. Again, you have no idea what you're talking about and that's why you're getting this reply. You could choose to think "I could learn from this" or you could continue to double-down and show further how the real problem is that you don't actually know this stuff.
It allows for PCs that wouldn't normally work together to team up.
So like a Rogue Trader game? Or a Dark Heresy game? Or what would be equally possible in any other area of the setting that you chose to do this on? If you choose to set your game on Holy Terra then no, you're probably not going to be easily able to hand-wave an aeldari working with the humans. But if that's something you want, just don't set the game on Holy Terra. What you just listed is not even slightly special to the area of the setting you don't want to use. So why list it as a reason you need to use that area? The entire specific combination of all the things you're listing isn't remotely special to the area of the setting. You could do the same anywhere you wanted to.
It has in universe loot, crafting, and progression in the form of collecting blackstone fragments.
It has "in-universe loot" and "progression"? Wow - now I understand why you must use this area of the setting. I guess you'll have to learn how to handle a player disagreeing with the setting material after all.
Seriously? Loot? Progression? "Blackstone fragments." Are we at the point now where WH40K's lore makes it inaccessible as a setting because otherwise players wont have "blackstone fragments"? (Necron Pylons are not unique to this area, btw).
Players who don't know what's going on are learning the mystery with the PCs. Those who do know what's going on still have to work through the campaign.
So like any campaign?
The nexus suppresses the warp, and by extension psy powers. In 40k that means most FTL tavel, long distance communication, etc. It's long been commented in canon that Sisters, who burn the mutant, the witch, and the heretic, have "miracles" that are the exact same thing they are trying to destroy.
Yes, I looked it up. None of it is any reason why this becomes a better region for an RPG campaign than any other region. You're deliberately creating problems for yourself so that you can say it's difficult. But it's not. People here would be more than happy to help you develop campaign ideas or location ideas. I would be happy to help. Or we could just point you at extensive published setting material actually designed for running an RPG campaign in as opposed to a mission pack for the table top miniatures game. But you don't want that. You want to complain.
As said above, there's a lot to like about the Pariah Nexus, for me at least.
None of your list seemed special or unique to me, not even the combination of all of them is unique. Frankly I wouldn't want to use it because the scope is FAR too big and I think most GMs would agree with me. If it's that consequential to the entire galaxy then you'd expect to see chapter masters, Necron Lords, Eldar Autarchs and Farseers. IME, most GMs don't want to run an RPG campaign at that level. That's more of a table-top thing.
But if you like it, go for it. But you can't say 'I want to use this specific element but a player might disagree with it so the setting isn't accessible and doesn't have good entry points.'
I'm not likely to run a 40k RPG.
Well that's pretty much obvious. None of what you post is looking for actual solutions, it's attempting to find difficulties.
Not 40k related, but I do see it as external because the problem is the local TTRPG scene is non-existent.
That's nothing to do with WH40K lore which is specifically where I said you were externalising your problem. In fact, it has nothing to do with WH40K. You said WH40K has "no convenient entry point". When it's pointed out that it's nothing but entry points and someone gives you starter entry points, you start shifting ground to say well no, you want to use this specific entry point. You give a bunch of made up reasons why, none of which make sense because everything you list is also found all over the rest of the setting as well. But fine - you want to use it you can, so then you have to start talking about how one specific thing with one specific faction that is entirely optional for a GM to include has people arguing over it online and therefore you can't run a WH40K game because "some nerd" might dispute it and you can't say that this is what the publishers wrote and you've decided to stick with that.
You might just be the biggest pussy this thread has ever seen. Quit blaming games for your issues. This isn't about WH40K. You do it with multiple good games. You start asking about a game or suggestions, then you find reasons why they wont work for you. Stop it.