Where do you want to see Dark Heresy go? Being the "entry level" 40KRPG, I don't think more Ascension level material is warranted. Perhaps an expansion for HIve Gang campaigns, or military action as Gaurd or Renegades. Maybe even a Mercenary supplement wherein rag-tag groups composed of Humans, Eldar, Ogryn, Kroot, Ratlings and Orks fighting in brushfire wars for a profit.
The Galaxy is a big place. Focusing on a single solar system might be a good time. I think Warhammer 40000 Role Play: Necromunda would sell out in hours. This wouldn't be a series where the core rules are reprinted, but each book would expand the scope within about 256 pages or so (the size of the Inquisitor's Handbook ).
Anyhow just a thought. With no word coming of Dark Heresy's future, and all the books in last year's Knowledge is Power now in our hands, speculation is all we've got.... I love this game system, and I see much more potential beyond the 3 core games. Heck, I'd even write Necromunda for Ross if he wanted it.
Hints that I'm right about something from THOSE WHO WOULD KNOW are very welcome.