From what I read the Rhodesians had a chance after World War Two to dramatically increase their White numbers from Europe but thought that such numbers would ruin their upper crust society.Rhodesia? If that hasn't been mentioned before...
Maybe Cecil Rhodes is able to bring in more white settlers into the nation prior to decolonisation?
It would be interesting if Ian Smith held onto power as South Africa went the way of OTL, leading to plenty of disaffected pro-Apartheid Afrikaners giving the Rhodies a population boost. Maybe the alternate fall of Portuguese Africa may lead to a pre-Carnation government-in-exile with White Portuguese coming over as well. I guess there might be some attempts at nuclear power/weapons should everything go pear shaped in SA?
Just my thoughts. Certainly wouldn't want it though...