I would like to state that I am very much in favour of this, though I believe the devs might have something like this in mind but are applying it gradually somehow.
Not meaning to steal your thunder, I would like to make the related suggestion that the 'Change Teams' selection menu have 'Available' set as its default filter, because the number of times I've had to scroll past my greyed out upgraded bronzes when looking for my weak silvers in a Gold Prize Fight is almost enough to make me go insane, while treasure nodes in Daily Events deserve their name just because it's a treasure hunt to look for the eligible characters among the sea of restrictedness.