People have asked in previous Q&As why don't we have access to playable Zandalari or Kul'Tiran yet. The response is, it needs to fit the story. Well, if you finish your respective faction's continents you received their pledge. Why not then? If not then, how about finishing the stories and then getting exalted with them? Still no... why not?
IMO they are delaying the next allied race purposely until it lines up with when most Dreadwake mount subs run out as another boost to revenue and nothing more. That means we can expect to see playable Zandalari and KT in March or April.