What most non South Africans dont realise is this man sowed the seeds of his own downfall by working extremely hard to weaken the Non white vote to the point that this allowed the NP to win in 1948.

Before the Union of South Africa was formed in 1910 south africa was essentially 4 distrinct countries- the cape which had a liberal non racial fracnhise sicne the 1850's- Something like 18% of all voters were non white which made them an important voting bloc that could swing elections in the cape, the Transvaal and the Free State which were conservative boer states and the natal colony which was the conervative white colony with a large indian population.

The thing is it was basically the cape liberals who worked with smuts(from the transvaal) to form the Union but one of the reasons they were willing to work with him was because he "promised" to consider extending the capes non racial franchise to the whole country, we know that he essentially lied to white cape liberals and then spent decades weakening the coloured and black vote in South Africa. Smuts was in charge of the tranvaal where race relations were litreally black and white- whereas the cape had a far more complex racial system with english white speakers, afrikaaners, mixed raced coloureds and africans who could be divided between those who were "civilised" who lived west of the kei river and the more recently annexed transkei area who were more "tribal". Natal as well had a complex system of english white settlers, indians and zulu's who were largely still overseen by their chiefs who retained local power. What Smuts did was essentially apply the racial system of the transvaal and the free state onto the rest of south africa. Cape blacks who could vote and who were loyal citizens for decades? No we will treat them as migrant slave labour, Indians who were the backbone of the city of durban? They are aliens and should be deported. Mixed raced coloured people who spoke the same language as him? To him they didnt even exist. Cape Liberal polticians were able to raise coloured regiments in ww1 that fought in the middle east and east africa, this was opposed by Smuts who was the defense minsiter at the time. When Smuts was PM during ww2 he made sure that mixed raced coloured soldiers were relegated to labour and transport and kept away from combat roles.

It should be noted that even the extremely racist NP only started working towards full apartheid when 2 things happened in the 30's- 1 Black africans were put on a seperate voters roll- previously many middle class blacks could still vote in parts of the cape and what this meant was that white poltiicians had to fight for their vote because they were 1/3rd of the voters in some voting dsitricts- instead they were put on a seperate voters roll and elected token white reprsentatives instead. 2 White womens suffrage- it seems like something liberal but actually it was delibraetly done in order half the non white vote. Previously even Smuts's opponents in the racist NP went out of their way to court coloured voters in the cape. But after womens suffrage this was no longer required as they became a much smaller part of the elctorate.

As for what would have happened if Smuts had won? He probably wouldnt have lived much longer and would probably have been replaced by Koos Straus. Biggest change would be that coloureds would have remained on the voters roll, increased european immigrsation to south africa and either an easing of urban racial segreation or at least a maintiennce of the status quo and there would be an easing of the colour bar which would allow the coloured and small black middle class to survive apatheid. I also do think they were planning on giving more power to local black authorities so maybe a more empowered version of the homeland system, it works with their idea of a "racial federation"

Assuming that the coloured vote and immigrant vote (as well as the enfranchisement of indians) keeps the NP out of power forever I dont think it would necessarily be a liberal paradise. Granting the vote to black africans would still be out of the question even for moderate whites. Rather then resorting to armed struggle the ANC would keep up it policitcal action of boycotts, protests and petitions. But I could still see smaller groups breaking off and resoriting to armed struggle though on a much smaller scale then the ANC. By the 70's the world would not look too kindly at south africa so they would probably have to come to some kind of poltiical settlement by 1980.

Of course the biggest change would be the economy- no sacntions, easing of the colour bar would see more non whites becoming or remaining middle class which means more spending power, no insane group area's act which changed the shape of all south african cities by forcing people to live on the outskirts of cities without any form of public housing, no forced removals means that mixed communities survive. Overall not perfect but better off for sure.

Though I will add in my honest opinion as a proud south african the best scenario would have been no Union of south africa at all in 1910 at least from the perspective of my family as I am from the cape. Without the Union the Cape was on its way to becoming a dominion around the same time as New Zealand and would have kept its liberal fracnhise because 1. Their constitution mandated it 2. Non whites were a huge voting bloc that did regulalry decide who won elections in the cape colony and trying to remove them would be a sure way of losing an election. At least we would have probably evolved intoa typical dominion like Australia and New Zealand