This happened to me at ORD a year or two ago. An aircraft change, I guess due to a mechanical issue, and we ended up with a plane intended for international travel. They had to download fuel for the ORD-LAX flight and it took several hours. One of those situations where they boarded the passengers on the plane, made us sit there for an hour or so, then took us off. I suspect it was to avoid having to recompense us at a significant level. I think we ended up having to spend the night and rebook for the next day.