AC is definitely the outlier here among NA airlines in not offering same day changes to their top tier members. However, I'd expect they collect millions in same day change fees, so they'd be reluctant to give it up.
The area where it could have a payoff would be in reducing oversold flights. I'm sure there are plenty of instances each day where a customer would prefer to move from an oversold flight to a flight with space, but doesn't because of the fee. One of the side benefits to free SDC's is that some customers on oversold flights would voluntarily move to flights with room, which is a benefit to the airline in reducing IDB/VDB compensation. The system wouldn't (or shouldn't) allow them to do a SDC to full/oversold flights, so any time a customer moves away from an oversold flight, it's one less potential IDB.
In addition to it being a good benefit for AC's frequent fliers, it could have some business benefits in reducing oversold flights.