There is an aspect of this incident which does not appear to have been discussed in this thread and it really is the "elephant in the room"; and the question that sticks out in my mind is
How is it that the Virgin flight crew only became aware of the fog at YPAD when at TOPD at approximately 2300Z?
This raises questions as to what procedures Virgin has in place to ensure pilots are updated on changing weather/NOTAMs once they have completed flight planning and now in flight, and also how effective those procedures are in practice. In the preliminary ATSB report, it is mentioned that the crew of VYK were advised by their company (through ACARS) that YPAD required an ALTN within 20 minutes of their departure from YSSY, which gave more time for consideration of ALTN options. I would propose that Virgin's late awareness of the need to hold an ALTN for YPAD may have limited the options available to them for a suitable ALTN.
Furthermore, it is also noted that both the Virgin and Qantas crews did not appear (according to the ATSB report) to be notified by anyone that MIA had also gone into SPECI at 2318Z after both aircraft had notified their intentions to divert to MIA.
So which agency holds responsibility for inflight updating of airline flight crews, particularly for significant weather changes - is it airline operational control, ATC or the pilots themselves through utilisation of Flightwatch services?
Looking forward to hearing from anyone who can enlighten me as to how inflight updating works for both Virgin and Qantas.