I can definitely see the need to have the 777x as a subfleet, but as a 1 for 1 replacement for the A380 would seem unwise.
The A380 once paid for (presuming they mortgage them like BA does with it’s 747s) would be a competitive aircraft to operate once it’s all paid off.
The question is oil. Is sub $50 oil here to stay, or are we seeing a blip and $85ish the right price? The new planes may burn 25% less fuel, but if fuel is 30% below predictions long term, is it worth buying expensive new planes, or keep older ones flying longer.
And would the plane rotate constantly between Sydney and New York, or Follow a more circular Sydney - New York - London - Dubai - Sydney rotation eastbound, and another plane doing the same westbound.
If they did that and got the timings right, the aircraft utilisation would be insane.