So, firstly let me preface this by saying aesthetically everything looks fantastic, the amount of detail put into the armors and weapons is wonderful and I adore it. Part of the joy of 40k is having all of this elaborate, ancient equipment - style points and whatnot, you know how it is.
There are still just a couple of things that would make for some very fantastic icing on the cake both from a gameplay standpoint and an aesthetic standpoint - maybe as endgame-esque loot. Specifically two little objects of great worth and consequence: the Iron Halo and sacred Rosarius. While the former is largely withheld exclusively for Space Marine chapters, considering the Inquisitors seem to be clad in their fancy-ass power armor anyway, and the sheer breadth of the resources that the Inquisition has access to, it wouldn't be farfetched to be able to attain one.
The Rosarius serves the same function but is often used by members of the Inquisition in contrast, so if we can't have the first (ideally we'd have both), it'd be great if we could at least get the Rosarius added in at some point or another. While there's no real point in adding something without a function in a game like this, even if it were just an aesthetic option available it would be good to see one (or both), modeled and actually added to the various suits of armor and such, because if it isn't reflected on the character model just about anything else would work fine.
From a mechanical standpoint (not that the following ideas will be any good, but they're something), it'd probably primarily either add some form of shield to take down prior to the healthbar draining, or just add HP or something along those lines - it would ideally occupy a new slot exclusively for things of this sort. Either the Iron Halo or the Rosarius could be chosen once acquired, but not both (I'm not sure that lorewise multiple refractor fields would function properly due to potential overlapping issues anyway). I don't know if it's actually feasible to actually add this into the game at this point, or to add the slot, or to have the items actually reflected in the character models considering most of the other idle little bits of gear isn't (although these would be much more consequential than purity seals and whatnot by their very nature), but it would be a nice thing to see implemented in some form or another, and I'm willing to bet a lot of people would agree. Because, really, the Iron Halo and Rosarius (especially the Iron Halo) are badass and iconic.