Unless they create some brand new primal/esper/GF/aeon, my guess would be either Valigarmanda (Tritoch) or Quetzacoatl.


We DO have a dragon "trapped" in ice in Coerthas West, in a location that happens to have a very peculiar name... "The Sleeping Dragon".
(Granted Tritoch was not really a dragon, but it did look like a bird dragon thing)