I'll ask the people who know a lot more about Africa than me (ie you and
@Gary Oswald for one): Would an "African Argentina" (ie, state with a majority descended from European immigrants that got that way almost completely through voluntary immigration) even be slightly plausible? From my limited perspective, it doesn't seem like there were that many Europeans willing to go there compared to the Americas, and you'd have to have them all settle an implausibly limited area, and other objections I haven't even thought of...