1: FRA-ORD / Already LH has one 747 and one A340 on this route daily. This route feeds into UA's domestic system well. I would invision them cutting the 747 and the A340 in favor of the A3XX once per day.
2: FRA-LAX or FRA-SFO
LH has 2 daily 744 flights to LAX, which proves that they must have enough pax for the A3XX, however, SFO fits better as a feeder for UA.
3: FRA-IAD. They already havean a340 and 744 on this route so the load and feed factors fit.
4: FRA-JFK....duh
But putting an A380 on these routes cuts against the pattern of flight planning today by most airlines, including BA, which is to provide more convenient frequencies with smaller aircraft. Particularly where slots are difficult but not an absolute barrier (e.g., not at places like LHR or NRT), airlines want more frequencies, not just more seats, because that's what pax want.
This is Boeing's fundamental argument against the superjumbos. We'll see.
Greg