Interesting read.
However, it doesn't take into account the other scenario for South African unity that worried the Colonial Office. This was that with the debacle of the Jameson Raid, the chance to center a United South Africa on one of the British colonies had passed.
Lord Selborne, the Undersecretary of State for the Colonial Office and Lord Salisbury's son-in-law wrote a fascinating memorandum in March 1896. It essentially suggests that the most important fact of the Jameson Raid was the lack of Uitlander support. The Randlords of Johannesburg- at least those outside Rhodes' circle- didn't need to support a coup against Kruger, because they already had money and population on their side. It was not a question of if the Uitlanders would end up with political rights; it was a question of when and how that would be achieved.
Selborne warned that if it wasn't achieved by British force of arms, the nightmare scenario would be the replacement of the insular Boer Republics with an English-speaking, capitalist government that would rapidly accrue the surrounding states through simple economic gravity. Crucially, with the completion of a rail link to Mozambique that bypassed the British colonies, not only would the state lose its strategic dependence upon British infrastructure, it would choke off perhaps the single most important source of revenue for those colonies. And unlike the ZAR, the British wouldn't even have the figleaf of a casus belli to prevent it. It would be hard to rally the Empire against peaceful English speakers getting their neighbors to voluntarily join a more prosperous state.
“The key to the future of South Africa is in the Transvaal… the richest spot on earth… [it] is going to be the natural capital state and centre of South African commercial, social and political life…. [the loss of rail revenues would drive the Cape and Natal] to the verge of bankruptcy, so dependent are they upon their rail revenue. It needs no words to prove what a powerful use could be made of this instrument in squeezing the British South African Colonies into joining a United South African Republic."
Selborne to Chamberlain, 26 March 1896
And again in October:
'“A Union of the South African states with it [the Transvaal] will be a absolutely necessary for their prosperous existence. The only question in my opinion is whether that Union will be inside or outside the British empire.”
Selborne to Chamberlain, 18th October 1896
In other words, the fear that motivated the South African War wasn't of the Boer Republics at all- it was of the people who the Colonial Office claimed it was fighting the war to protect...