The art book includes a quote written by Mike Simpson of Creative Assembly;
These games are being made by a new team specifically for the Warhammer property and won’t be taking away from the historical titles such as the upcoming, Attila. While we haven’t seen magic in any previous Total War titles, it is likely Sega will have no problem adapting to the franchise with their experience in medieval warfare simulation so far. This doesn’t include the 40K universe yet, but one can hope.