Just a thought...

I have, on occasion, seen it said that there are actually several different iterations of the Old World setting: that while many of the names are the same, the world of "Warhammer Fantasy Roleplay" is not the same world as "Warhammer Fantasy Battle", which is not the same world as "Bloodbowl".

It seems to me that Games Workshop/Fantasy Flight Games would do well to make a similar distinction between the setting used in "Warhammer 40,000" versus that used in the various RPGs in the same 'universe' - "Dark Heresy", "Rogue Trader", "Deathwatch", "Black Crusade", and "Only War".

The fundamental issue, it seems to me, is one of hand lines - in the wargame you want single, monolithic forces with little or no intermingling. That is, you have a Necron force, a Chaos Space Marine Force, an Eldar force, but no "mixed parties". However, in the RPGs, and especially in the likes of "Black Crusade", that can be somewhat problematic - interactions between a band of BC heretics and, say, a group of Orks are almost inevitably going to be at the point of a bolter. There's no intermingling of cultures, which means there are very limited opportunities for interaction. (And it's actually worse than that - about half of BC heretics are obviously and unmistakably enemies of the Imperium. This means that any scenario where they are expected to travel undercover through said Imperium are essentially doomed before they begin. This could be fixed by having Space Marines 'retire' from active service, and so appearing occasionally in the various strata of society, but that appears not to be a feature of the setting.)

(In fact, should I run "Black Crusade", I'm inclined to do exactly that - have a somewhat variant version of the setting in which the cultures are much less monolithic, much more factionalised, and much more intermingled. Oh, and while the Imperium is both powerful, oppressive, and omni-present... I'll be vastly reducing the actual level of surveillance while also ramping up the level of paranoia.)