Check out the patch notes for the v20 Lovely Update here: http://maplestory2.nexon.net/en/news/article/55909/lovely-update-v20
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If NPCs wearing corsets and skimpy clothing bothers you to the point that you think it should be removed then maybe this isn't the game for you. If it makes you feel really uncomfortable it would probably be best to just not play the game anymore or try to ignore it. I doubt Nexon would remove official clothing like this considering it doesn't really seem to bother most people and none of the NPCs seem to push the13+ rating.
I think it's pretty reasonable to have clearer guidelines on what is considered too sexual. This way you won't get people getting their items taken down for having a shirt that shows a bit of cleavage or a bikini top. The people who make these items aren't trying to break the rules, they see official items like swimsuits that give you big breasts and bunny girl NPCs and think it must be ok since the game has official content similar to what they want to make. As long as you aren't making something like fetish gear you should be fine.