As previous posters have mentioned, from 2008 QF have been waiting on the 787s.

I'm sure they considered leasing/purchasing some 777s in 2008 when fuel prices were high and it became apparent that the 787 delays were significant. However given the 787s delays were rolling, and it would have taken some time to get a sizeable number of 777s into the fleet it probably was not a a viable short term option. Demand for the 777s since 2008 has been high given its efficiency over other similar sized a/c.

I think its more interesting to note that QF didnt order the 777 back in the 1990s when they quite clearly had a gap in the fleet between the 767 and 747.

Who knows, they might have ordered some 777-200s, grew the network and they might have been more inclined to order some later model 777s when the opportunity arose.