T-VASIS
As you suggest the B777-200LR can operate LHR-PER with a full pax load and 15 tonnes of cargo. PER-LHR is viable year round provided there is no expectation of cargo being uplifted.
At some stage in the near future QF will have to go back into SIN-LHR by overflying DXB or operate PER-LHR nonstop due to political/religious problems mounting in the Middle East.
There is already evidence of QF losing LHR traffic to other carriers, especially high yielding traffic who do not wish to transit DXB. In an attempt to keep the premium cabins full QF are now contacting J class pax with frequent points available offering a transfer to F class. This is in addition to contacting Y class pax with frequent points available and offering a transfer to J or F.