Why they picked those two for the starter set(s), I'll never know, Empire civil war, Empire vs. Chaos or ye olde Empire vs. Orcs would have made more sense, but what do I know....
If they're not even going to officially support long standing traditional armies like Dark Elves, Undead (VCs) or Skaven, why would there be separate armies for Kislev or far, far away Cathay ?