An IOSA certification is no walk in the park and I personally feel that the CAA have gone overboard in grounding Nationwide, especially their B767 operation. Also, the timing of the grounding is questionable. This probably has a lot more to do with the pressure the CAA is under from the FAA than anything else, and Nationwide is the sacrificial lamb.
There are many African operators flying into SA airspace with aircraft which would not qualify for Part 91 ops, let alone Part 121.