The Bemperor
That said, I think they should focus on the Guard or even the Arbites. Have Marines just come in like a wrecking ball at some point and DEMOLISH some xenos but mostly tell the story of regular humans.
I’d love a Ciaphas Cain series but it doesn’t seem likely.
There was talk of Eisenhorn being serialized. No idea what happened to the project. The mobile game has shown the story is there and can be made into a movie (i.e. if you ignore the shitty gameplay and stabbing powerswords through doors and only focus on cinematics, it’s cool).