In principle, ethnic homogeneity is usually a good thing for a country's development and stability. However, it is often very hard to draw clean borders between ethnicities in Africa, and I think most major cities are multi-ethnic by now. This solution is just not practically feasible. Perhaps a better idea would be to gradually adopt the neutral lingua franca (English, Swahili, French) as a native language, thus allowing a national identity to develop across tribal backgrounds.