You hit the key fact here: operating cost. The 787, especially with the larger -9 model, has seat costs similar/lower than the 744 (and maybe even match the new 748i) and beat the 380. That is why there hasn't been exactly a rash of orders for these larger planes recently, LH is the only one who has ordered the 748i (who also don't have orders for the 787), and well, people aren't exactly banging down the door to get the 380 since its initial rash of orders, whose economics have since been trumped by the 787.

With much lower costs, airlines can make some routes work with the 787 where previously, it was the domain of much bigger aircraft. It can fly more frequencies (convenience factor for biz travelers) to get the same number seats on the route.

What does this mean for CO and return to AU? Its possible, and maybe even profitable, but I think CO has bigger fish to fry first before thinking of flying IAH/LAX-SYD.