Nobody has bothered to tell us which version of 777s we are guessing about. If Boeing are offering them very quickly, are they somebody else' cancellations. If they are 777-300ERs, those are substantially larger than the 787-8s that JQ thought they were going to have. Would Boeing offer new build 777-200ERs, 10 years after the type entered service? 777-200ERs are Windows 95 planes.
777-300ERs are a bit big to fly around the region - Phuket, HCM, KL. Even for Qantas mainline, the ER is a bit of a waste to HKG and Tokyo, when the non ER 777-300 already could do those sectors (and Qantas could do an engine competition as well.) The 777-300ER seems like overdoing it for lower yield flights between Australia and Southern Europe.