The A380 is simply too much plane for pretty much any of UA's routes - SFO-SYD is actually one of the few where it has the best chance of working, but you don't order a plane because it would be nice to have on one route.
The A380 would do well on the following UA routes:
Currently served by a B772.. wouldn't the B788 or B789 (whichever they're ordering) fit here?
United's international 777's seat, according to seatguru.com, 252 and 253 passengers.
United has ordered both the 787-8 and 787-9. The former, according to Wikipedia, seats 242 in 3 classes while the latter has 250-290 in three classes. I haven't seen anything on how United is going to configure their 787's.
Tokyo (NRT) is served by both the 747 and the 777 from California. SFO gets the 747 service (once daily) while LAX has twice daily 777's.
So did AWE, when they bought their B742 for US West Coast to Tokyo service via HNL. It tanked.. BADLY.
AWE served Nagoya, not Tokyo, and they had 3, not 1, 747. They discontinued the Honolulu/Nagoya segment and sold it to Northwest.