Re the 787-9 - LATAM seem to manage to do SCL-MEL/AKL no worries, but then again they have 330min EDTO, which the A/C is capable of but the question is will CASA allow it?
I agree if they got 330 min JNB wouldn't be an issue but the T/O performance out of JNB could be, the twins don't like hot and high, which is one of the reasons why the A340 was a popular machine ex JNB. Not sure about the 787 performance, but the 777-300ER is v payload limited when it's hot/vs high, far more so than the A330, at least in 200 guise anyway.
From the airbus site looks like RUN and MRU are A380 capable - but as someone pointed out, vs a 747 thats a LOT more seats onto the market with a lot more fuel burn. Interesting times!