I was curious after reading this and looked at some example fares going in late Dec, returning early Jan (ex NYC): Y going for ~$2300, C for $10,000, F for $18,000. Amazing, and I wonder if real people buy these!

If so, and I were at United, I'd add any aircraft I could! another 747 LAX-SYD, then if no more 747s available, 763/777 HNL-SYD (or AKL-SYD).. anything to cash in on these fares while they can get them!