...40k books SHOULD go on /lit/, though.
Black Library books have either very little in common with the actual tabletop games (Dan Abnett) or NOTHING AT ALL AND OWE EVERYTHING TO THE VIDYA (C. S. Goto).
They have MUCH less to do with 40k than Record of Lodoss War has to do with D&D. Have you ever seen a thread specifically about Record of Lodoss War on /tg/? I've seen them on /a/, but not here, just as it should be.
By the same measure, Gaunt's Ghosts and Ciaphas Cain should be discussed on /lit/.
Having a traditional game involved at SOME point doesn't make something /tg/-related.