The hot rumour doing the rounds was that QF were looking to get 8 - 12 ex United 747-400's. No doubt this would give them 2 more flights into LHR daily, and extra capacity to add to the USA.
It would also give QF a full-house of 744s
RR powered 744s
GE powered 744s
PW powered 744s and
GE powered 744ERs
Realistically you can't imagine QF buying more 744s, especially older examples with a completely different engine type. It might be reasonable to suggest that they could lease a few until the A380s arrive but even then you'd think they'd want to outsource the maintenance of the PW powered birds to someone like SQ, TG or UA.