I blame this entirely on all the 2024 snafu where AC mailed 75k to a large # of passengers in error. Clearly they were overusing this benefit

AC could have tweaked this benefit by stating that any SE on oversell standby at T-6hrs will have best efforts accomodation and perhaps a call back with updates before airport arrival. When we used this and booked at T-6h, we had issues getting seat #s at the airport outstation. The concierge I phoned told me that she a teammate right next to her had been proactively phoning other pax due to our oversell, and had just freed up the first of our seats as our call came in ("another passenger we called wanted to fly tomorrow").

A US ULCC recemtly emailed me a few hours before my flight, stating that the system noticed I had not checked, and offered a free change or cancel due to my flight being full/oversold. United regularly asks what amount I would accept to volunteer during online checkin.

If AC wanted to take away a benefit that comes with $20k a year in spend with no notice period so early into the benefit year, they should offer something in return. An extra select benefit / priority award / or significant SQD+SQM bonus for those who have ever used this back pocket benefit would be the right thing to do.