So, if they did a final pass, which is seeming unlikely, likely choices seem to be:
Italy for a European DLC, Maybe paired with Ireland, or Switzerland, a Kalmar themed Denmark, or Bulgaria (Or Goths, as I would hope)
Morocco for Africa, maybe paired with an Egyptian alt-leader (Ramesses probably, but preferably some more overlooked leader for the series),
Assyria, probably under Ashurbanipal, from the Middle East,
Hawaii and the Iroquois for a "native" pass (that's the best name I can tie them with off the top of my head)
Siam, Burma, or Afghanistan for Asia,
Maybe Madagascar or Kilwa for Sub-Saharan Africa, to wrap the game with options that I've seen thrown around quite frequently.