Difficult one to predict and I'm certainly no expert. I imagine Qantas and their low cost subsidiary Jetstar will open up new direct destinations in the US over the coming years. Jetstar have just launched routes to ASIA at ridiculously low fare prices so if they follow that strategy to US, it would really shake things up.
Like you mention, UA don't (and won't in the medium term) have the equipment to compete on any new direct destinations from OZ-USA. But their US domestic network is so strong, which will undoubtable hold them in a strong position whatever way the market shapes up.
Cheaper fares (ala Jetstar) and varied new services/destinations may well stimulate loads. Both UA and QF seem to currently have close to full loads on their limited services OZ-USA, so I recon there is definitely some room for increased traffic between the two. Not sure what city pairings would be involved though...