Westbound RTW ex-Africa were always OK since one could return to Africa via Asia or SWP. Eastbound RTW ex-Africa required 2 passes thru Europe one of which must be a transit thru Europe enroute to Ghana/Nigeria/Kenya/Tanzania/Uganda. The addition of the Comair JNB-MRU flight would allow an eastbound RTW ex-MRU since you could get to Asia/SWP without going thru Europe.
By the way, I have not found the JNB-MRU flight on ba.com or any of its associated sites.