Playing to the far right part of the fanbase of 40K would not be a good idea, there very vocal online but wouldnt amount to much, go fash, lose cash.
Really I think besides the scale of the thing getting that tone right is the main issue, not making the Imperium either too nice or simplistic badguys, making Chaos genuinely threatening, etc.
Again my feeling is there best off starting fairly small and getting bigger and bigger, adding both a wider setting and more layers tio the mythology rather than trying to dump everything on the viewer at once.