do you think that UA or any other legacies, as part of the whole $25/extra bag sort of thing, might eventually slap restrictions on same-day standby as a way to generate revenue?
I.e. if people want to be able to change their flights, there is some profit being lost by letting them do so for free.
US Airways already does this. $25 fee just for the privilege of getting on the standby list. You might not get on the flight, and still lose the $25.