Its not just a lounge issue. Its also one of gate availability at the morning arrivals peak time. But T4 will not be getting A380-capable gates any time soon, so A380 services will be TBIT or remote stands and busses.
NM, you're on thin ice talking about buses
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Taking your point though, I suppose we can assume there will be no A380 services between SYD and LAX unless QF cut the amount of a/c arriving into LAX to accommodate such. Or, arriving SYD pax will have to do the long march through the tunnel to T4 immigration from TBIT.