If there are the Egyptians, Carthaginians, Nubians, Ethiopians, Mali/Ghana/Songhai, and Zulus, in Civ4 or the next Civ3 expansion pack (after C3C), there shouldn't be any need to add more african civilizations. But until then, the African continent will be empty and not have all the civs that deserve to be recognized.
I'm not saying that all the african civs are more noteworthy than other civs, I don't know that much about them to say anything like that. But I do think that they should eventually all be civilizations in Civ4.