I think they will struggle to get the 777-200LR JNB-ATL with a decent payload (with any payload). I can foresee them making unscheduled stops in Dakar (or even Sal or maybe even Cape Town) relatively regularly!
Interesting that they are moving the CPT flight to ATL and reducing the frequency to three times a week (from four) - it is still a net gain in capacity! I think ATL gives them better connectivity in the US and since the JNB flight is no longer stopping in DKR they do not need to have the connecting option there!