Years ago, I had an idea that if the Gold discoveries that sparked the Georgian gold rush in OTL had been discovered earlier, enough white colonists could be brought to the colony to solidify an anti-slavery consensus in a similar way to how the California Gold Rush created an anti-slavery movement in OTL. Given that there was a
Brazillian Gold Rush going on from the late 17th century, it's at least somewhat plausible IMO.
Of course, the problem of the malarial lowlands is still there. And there's the issue of what happens once the Gold Rush peters out. But with the right political leadership...
Such a POD would also drastically alter the development of the American colonies as the Georgian discoveries would likely lead to numerous prospectors exploring the region, resulting in earlier discoveries of Gold in Carolina and potentially Maine.