I get AC tries to make it work and if that were to happen to me, a reschedule to another flight is not a big deal as I only fly on vacation and I like airports (weird I know) and I can live with a few extra hours in the lounge.

I still think AC gets away with quite a bit based on some of the stories I read on here. My work lawyers would never let me implement a product where we advertise a core benefit that we can then just take away in the T&Cs (T&Cs may reduce inherent risk assessement but never eliminate it) and instant eupgrade is clearly advertised as a core benefit for Lat. The bank regulations and consumer laws are pretty strong (too strong IMO) and part of the remedy always includes building a process to make clients whole.

I have had conversations with our lawyers and outside counsel where they basically say any exceptions that take away an advertised or expected benefit need to be prominently displayed to clients and T&Cs don't cut it. Reason is otherwise it's a bait and switch. There are also marketing rules where if a feature gets used as a selling incentive then there are rules on how you need to honor it.

No clue how tight and client friendly airline regulations are but I think a client who gets downgraded with no recourse offered would have a pretty good case in court. Then there is the whole risk of class action, bad PR (though airlines seem imune) and tighter regulations to weigh.