I see I missed about fifteen pages of this thread ...
If you want to fill in a bit of the gap in Africa, then I return to my suggestion of Orange Free State, with all its advantages. As various people posted, lots of civs committed bad things in their history, so the Boers are hardly uniquely bad.
About Bulgaria - I should just pass on a little story. A couple of friends of mine met a woman who was a passionate Bulgarian nationalist. The Bulgarians, she claimed, were responsible for every good thing that ever happened in history. My friends said, well, what about the Ancient Greeks and their scientific and cultural developments? "Hah!" said the woman. "They were just proto-Bulgarians!"
For Africa, I think after Ethiopia if the devs want to add more Civs, I think a Swahili blob, Zimbabwe, Ashanti, Dahomey, Morocco/Berbers, or Benin should come first. I really don't want any more colonial/post-colonial nations. Especially not for Africa.
Someone also posed the question of how your list would change if we had two "Frontier Passes". For me, quite a bit actually. My best case scenario for the current Frontier Pass, based on what we know, would be Maya, Gran Colombia, Ethiopia, Portugal, Byzantium, Babylon, Austria, and the Cherokee, plus William of Orange as an alternate Dutch leader.
However, if we have two passes, that changes things. For the first pass, I'd want to see the Maya, Gran Colombia, Ethiopia, Portugal, Babylon, Cherokee, Thailand/Sukhothai, Byzantium, and William of Orange as a Dutch leader. In the second pass, I'd like to see the Iroquois, Austria, Italy, a Swahili Civ, Vietnam/Burma, Assyria, a Western-North American Civ (think Apache, Sioux, Navajo, or Chinook), Celts/Gaul, and an Egyptian alternate leader. Normally, I wouldn't be too happy with Italy or the Celts if it meant that we'd miss out on say, Austria, a Native American Civ, or Babylon. However, if we'd get two packs, I'd be super happy to see those in the game. I guess it's just an order of priority.