It is possible that the Gods derive some of their power from the turning of the Cycle, and that this turning occurs because of each of the Houses acting according to their natures when they are in control of the Empire. For example, Zerika, as a Reborn Phoenix, is bringing about the rebirth of the Empire. Perhaps when all the energy needed has been put into that endeavor, no more energy is generated for the Cycle, but the Cycle turns to the Dragon, and then it becomes Norathar's responsibility to act as dictated by the characteristics of her House to continue to cause the Cycle to turn.
Why would this matter? It could be the justification for the prohibition of inter-House marriages (and the potential of crossbreeds) such as that between Piro and Ibronka, or Shant and Lewchin. Perhaps the "pure" characteristics of the Houses are needed to power the Cycle, and hence the Lords of Judgment, who protect the world of Dragaera from the Jenoine. And, as Zerika is the last surviving Phoenix, this issue could be forced if the Cycle is to survive another turn.