the reason why our game could grow up and have such an enormous scale today is mainly because how conveniently we can act in this grey (or black) area and how strong the propagation force of osu "gang" is
to be honest even 80% (years ago it was 90%) of the people in this game are "gamers", our game is literally feeded by them so i guess that is why we've never done anything really against them and make them unhappy
even i don't really think mons' post is 100% related to the topic but i do agree that he brought up an important point, that is we strictly forbidden any contents in the map that are not free to use to be submitted in our written rules but we pretended that it never exists for a long period of time
my suggestion is
1) either you delete/modify the rule mons posted before you implement your proporsal (as a rule/guideline or w/e) because just adding such a suggestion won't be able to solve the core problem of the contradiction between our submission rules and what we've done for years, or
2) just pretended nothing is happen and use your good persuade techniques to comfort any artists who feel offended or even made them fa (peppy stated that any artists who don't feel like to see that their contents are being used here without their permissions can always contact him) as what we've done for years, too
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there's another radical option but i don't think you'll really do this (that is the optimal one for me, though) so i'll just post it here as a possible reference:
considering "gamers" would just keep harassing artists whose songs are made into a hyped osu map and potentially make more and more of them become angry (the large portion of them don't because we are lucky, not because that is not even a thing), which i believe staffs won't be happy to see, so i suggest that we can
3) delete all submitted and ranked maps without permission from original artists (you can just let those who've asked for permission send you an email in a certain period of time, so their maps can prevent from being deleted - then you can delete all maps that are non-fa + holders of which are failed to give permission from artists), that can also become a wonderful chance to rework the reward mechanism in this game, for now it means the whole pp system (that would be another story, though)
if we can't legitly tell every osu "gamer" what is the manner, then i think it'd be best for staffs to either just pretend not seeing them and let the game grow (cuz grey area never actually matters, right?) or give them a serious lesson that their inappropriate behaviors would pay, adding a perfunctory rule or suggestion won't really help