besides the ones you mentioned, there’s a few others i’d suggest
Benin, being the kingdom of the Igbo, could be substituted for the Kingdoms of the Yoruba or Hausa (the other major ethnic groups of Nigeria) to represent West Africa.
The Jolof/Wolof empire would also be a good choice, occupying the weird niche of neither being exclusively an arab-speaking Saharan empire nor a subsaharan kingdom, as it geographically and culturally fills the gap between the two.
Ashanti, Oyó, Kane-Bornu, Somalia, Madagascar and Swahili, I also agree with.
Im iffy on Ghana the medieval kingdom just cuz geographically and playstyle-wise, i can’t imagine it filling a different niche than Mali—same reason why I wouldn’t choose Songhai (although in an ideal world where city list overlap was better addressed by Civ, and abilities could have more nuance to them, I’d love all three). Likewise, Angola under Ana Nzinga is appealing if not for the fact that it was a client state of Kongo under Mvemba and probably should only appear in Civ 7
Medieval Almoravid Morocco, the pre-Islamic Berbers or Modern Algeria would all be varying timeframes of the Berbers which, to me, could all have their perks to playing.
We also know far less about Medieval Zimbabwe than its successor state, the Mutapa empire, so I’d posit that as an alternative.
The kingdom of Buganda in the Great Lakes Region and the Swazi would also be interesting, although the Swazi, geographically and mechanically, don’t have much to offer different than the Zulu, so perhaps in Civ VII we can see them (I do disagree with the notion that South Africa’s largest indigenous group and most spoken indigenous language, not to mention its most historically prevalent state is historically irrelevant or unworthy of being a mainstay in the series though).
Burkina Faso under Thomas Sankara , Botswana under Seretse Khama and Tanzania under Julius Nyerere are intriguing post-colonial test-cases as uniquely successful states (under those specific leaders), and while none of them really qualify as a civ (and Tanzania specifically would be better represented by a Swahili civ), they’re all unique cases that I wouldn’t mind appearing as representatives of the contemporary era in Civ.