I don't know about that, I think that African settlers will still come once agriculture is established on the Mozambique coast. However, without the rice culture established by the Austronesians (I don't see African rice making it to Madagascar, just yam and millet agriculture) large parts of Madagascar won't be very useful to the African settlers, which I suppose could potentially open up land to a European settler colony. But that colony will probably resemble Zimbabwe or the highlands of Kenya rather than the Cape or North America.