Well, Cushitic peoples IOTL made it as far south as Tanzania IOTL:I don't like giving a boring answer, but my suspicion is that the most likely alternative is that another neighboring people in West Africa, such as one of the other Southern Bantoid groups, takes the same technological advantages and follows mostly the same expansion route.
https://en.wikipedia.org/wiki/South_Cushitic_languages
So, East Africa would most likely be Cushitic-speaking ITTL.