Alot of these ignore the fact that the Royal navy stands squarely in the way. there is no way for the Germans to help support the Boers. They'll never be able to get their (the key to British imperial success).
I like the invasion of South Africa in WW1, but it is unlikely, for the same reasons. The Martiz Rebellion was never going to take off. The Boers were already basically in charge of South Africa, what could they hope to win? And the German didn't have the logistical ability to go and actually invade South Africa.