We know that when the Dutch established their first colony in Cape Town in what is now South Africa, they started importing Malays amongst others to be their slave labor. However; there had already been an extensive but [at the time] unheralded series of migrations by Malays that mostly encompassed the South Pacific [most prominently in New Zealand, Tahiti, the Hawaiian Islands and Easter Island] but it did extend as far as Madagascar as early as 500 A.D.
Hence, my challenge to those interested would be to see how been plausible for these descendents of Malays who'd settled in Madagascar to have extended their holdings further and established a colony centered around the Cape of Good Hope before the first indisputable European siting by Bartolomeu Dias.