Look again at my map from earlier. Considering the southern option.
Diego Garcia is the dark patch mid-ocean between Thailand and Madagascar.
If the plane reached the red circle (where ping was) by 8:11am (after being near Phuket at 2:15am) then it was within the blue circle by then (time and speed limit).
Thus it was not heading for Diego Garcia, or Africa.
After perhaps rounding Sumatra and turning South, it was headed for Antarctica, due South, or just perhaps French Antarctic Islands, Heard Island or maybe even Perth, or inland Australia.
It is a pity that the Australian radar (white circle) was probably off for the weekend.