Before jumping up and down on the court, consider this. In somewhere like the USA (with extremely sophisticated lawyers to spin it) there could be a case made in court for kidnapping!
The aircraft was IN FLIGHT before passengers were told of the change. Not a diversion, a planned change. The circumstances seem to be that the airline made a decision to only tell the people on board after departure when they had no choice but to continue to the new destination.
By forcing this upon them, and removing their choice to not travel, then the passengers were taken against their wishes to a place they did not want to be. That sounds like it could be constructed into a kidnapping charge to me.