Retinue members and ancillaries have been part of the Total War series since the first Rome. Which ancillaries do you expect to see in Warhammer? I'm talking about ancillaries that are specific to the Warhammer world. We can probably assume that mundane items/retinue such as trusted servants, surgeons, and the like will be included.
Priestess of Shallya: All units in army are immune to disease
Priest of Myrmidia: Increased melee attack for all units in army
Witch hunter: Increased order through entire province
Tilean pistol: Either increased success to assassinate or decreased chance to be wounded or assassinated
Halfling cook: Increased morale