Much laughing and carry on was done when Boeing launched the 747-SP for trans pacific ops. Every one said it would never work long term. I think they got that wrong.
I believe it is inevitable that YSSY - LHR non stop will be the norm.
So the question is, how much of an efficiency improvement will they need to make Sydney to London direct on an 8x airframe.....and later a 9x airframe for the 777. Can the 777x generation of engines be incrementally improved enough to do that, or will it need a new generation of engine. The aim is not to have to reduce revenue payload to fit in underfloor tanks in the hold.