When you look at when CA usually announces major titles (not sagas or dlcs) they usually always do it towards the begining of the year over the last five years.
Total War: Warhammer.............22 April 2015
Total War: Warhammer 2.......... 31 March 2017
Total War: Three Kingdoms...... 10 January 2018
With Total War: Warhammer 2 the announcement trailer dropped and then six months it was released. So if they plan to release it in September/October they may announce it March or April again.
So might we be seeing a video drop over the next couple of months concerning the final in the trilogy. What do you think?