Now don't get me wrong; I love the Warhammer Total War games and I have enjoyed the historical ones I have played as well. It is more than likely they will continue doing both (with fantasy, it could be anything: 40k, AOS, LOTOR, maybe even GOT). But this thought occured to me and they could realistically do it.
What if CA decided to go and make their own IP and thus creating their own unique game in the Total War format? For example, let's say they decide to do their own fantasy styled game with all sorts of different fantasy races fighting in an unique setting of their own design.
It could be interesting, to say the least. Creating their own game universe means they don't need to get licensing rights from others, and it'd be their own complete creativity. Without the restraints of rights or following the lore of another company, they could have full freedom to make a completely exciting game of their own.