However , the question would be what a court would say on such a situation where the aeroplane to operate a flight was available, but the airline decided to cancel that flight so that the aeroplane could be used to replace a flight being operated by an unrelated seroplane which was impacted by weather

I would have thought that there would be a decent chance that it would be ruled as a purely commercial decision rather than actually being cancelled due to weather conditions

It would require taking it to court - unless this is the sort of thing that could refer to DOT

It is a shame that more regions do not have the protections that the EU provides