Max range and commercially viable operations are often two very different things. Again, lets look at some nnumbers.

From Boeing, for the 777-200LR we find:

MTOW = 766,000 lb
MLW = 492,000 lb

This means the max fuel burn before the operational payload is reduced will be 274,000 lb. But we must also allow for about 18,000 lb of fuel reserves, dropping payload to 256,000 lb.

Fuel burn for a 766,000 lb aircraft (with GE-110 donks) will be around 22,000 lb per hour, reducing to about 15,000 lb as weight approached MLW. So we can assume an average fuel burn of approx 19,000 lb/hr. This gives us about 13.5 hours flying time before payload is restricted. With an average cruise speed of Mach 0.84, (600mph) we get about 8100 miles (or 13,000km) in still air.

With the three additional optional fuel tanks in the rear cargo hold, max fuel capacity goes up to 358,048 lb. Now assuming our landing weight is going to be reduced to about 408,000 lb and hence the average fuel burn down to about 13,000 lb/hr or an average of 18,000 lb/hr. So with that much fuel we should get a flying time (with 18,000 lb fuel reserve) of approx 18.9 hours or about 11,000 miles in still air.

But what does this do to payload? Empty operational weight is 320,000 lb. So our payload is now down to 88,000 lb. Using my guess at 350 lb/pax allowance, we can get approx 250 people on board. Boeing quote a typical 3 class config as 301 pax, so we can constrained by approx 50 seats.

So, yes it can be done. But the issue is around the commercial viability of introducing a new type for a specific route. The other thing that comes into play is the hubbing efficiency in Asia, allowing QF to hub flights from BNE/SYD/MEL/PER/DWN etc into SIN and the mix&match passengers onto the European destinations (LHR/FCO/FRA/CDG).

They could probably fill a daily 772 with 250 pax between SYD-LHR. But that a new type for a specific operation is not likely to be viable. Given QF's current move toward Scarebus (acknowledging the recent post about looking for another 10 744's), perhaps the 777 is not overly attractive to them??