I mean, admittedly I need to add some kind of gallery where you can see the ones you've collected (basically a CS-Dex)
yes please, that would actually be amazing.
My issue with this would be that for completionists who like to have full living dexes, adding a CS Dex of pokemon that cannot be obtained anymore without trading would make it impossible for some people to complete theirs as people would be very hesitant to trade something like that.It could be argued that this is already a problem for some considering they‘re in the game, but that problem would only further itself if they were put in the/a dex