I like this idea, and in my recent experience a system for honoring confirmed U seats already exists: I was making a change to a ticket with two upgraded segments, requiring to reprise one of the components while keeping the same flights. This would cancel the upgrade but I was told that they can immediately reconfirm it although 0 availability by calling “the other department”, and that this was standard practice.

At the same time, we are still talking about the airline which managed to quote me 3 different prices within an hour for a ticket change, with all fares being significantly higher than ones broadcasted online... So I am a little sceptical about this kind of “confirm J award, change to rev Y + upgrade” would work within AY IT