Addis Ababa would be a good choice for A3.......Ethiopian is also a Star Alliance partner, so you would have hubs at both ends.

One of the most asked-for long-haul flights in Greece, is Johannesburg......but SAA is not in a position to add JNB-ATH, and A3 doesn't have any long-range planes.

Having ATH-ADD would take of local traffic, and connections to JNB, NBO, and other African destinations, using ET's network.