Flying into JNB this afternoon from Harare, we arrived at the same time as Air Mauritius, Etihad, Emirates and probably some more.
I have never seen the arrivals area so crowded. The lines stretched all the way up the escalator to the jetways and to the doors for the bus arrivals. There were signs up apologising for the delays due to biometric rollout. Lots of airline staff walking up and down checking if anyone had domestic connections so they could pull them to the front (via the crew/diplomat line).
After about 45 minutes and barely moving, they abandoned the idea of biometric collection and the lines began to move much faster. I made it out about 75 minutes after landing, but there were easily 500 people behind me in line and more coming in with every arrival.
So yeah, sounds like the worst fears have been realised.