It used to be that when a new aircraft type couldn't be delivered as promised & there was a similar, suitable alternative, that these would be offered on cheap leases until delivery of the ordered aircraft was achieved. There would also be no penalty when they were handed back as the ordered aircraft were delivered. Perhaps this doesn't happen now, or perhaps Qantas rejected the offer.
A 777-200LR or even a -200ER would have probably been a more than suitable alternative & most of the problems & costs associated with the delayed delivery would have then been avoided. Another upside would have been that QF would have been able to see if the aircraft would have suited their operation or not, for very little cost.
If this had been done, you may well have seen the 787 order converted to 777's of various marques, given all the advantages of the thing.