Ethiopia would be a fine and worthy civ, but not representative of the dynamic that was Bantu-speaking sub-saharan Africa.
The Bantu (or more narrowly, Zulu) in the game are on par with the Celts and Scandinavians (and arguably others, especially the non-included Polynesians), in that they didn't possess a true empire, but rather experienced a period of great expansion and military might through the advance of numerous related tribes and kingdoms. This makes them significant. That they reached the societal stage of Feudalism is indicative of their great expansion, in addition to the huge geographic spread of their languages (much like the Celts and Scandinavians). It's interesting that they also had "berserker" like characters within the militaristic apex of their society.
The Ethipians and Songhai are different. Older, more stable, and smaller. Part of the greater Mediterranian and Mideastern trading realms.
The Zulu, like the Iroquois and Maori (Polynesians of New Zealand) were on the "verge" just as European colonialism intervened. It's fun to imagine what might have happened otherwise, and I think that is a central appeal of Civilization to all of us!