350s are twin engines, can't fly to South America or South Africa because they'll fly over areas more than 3 hours from a useable airport. They can only send 380s (won't fill them) or 747s to those two continents. 

South Africa or South America*

Except, the 777, 350 or 787 doesn't offer any answers to what will they fly to South America and South America once their current 747s are retired. The only option seems to be 747-800s to comply with aviation laws.