Hahahahaha, try copyrighting a player skin in PG3D. There's always going to be copies of it wherever you look, regardless of what law is in place.
In any case, selling skins might not be a bad idea. On that note, the players should be able to only sell their skins with the price in coins (NOT gems). I believe in addition, they should add a coins-to-gems converter. It may not be a highly effective compromise, but I've seen it done before many times, both working greatly for the community (100k in-game currency for 50k premium currency), and working terribly (100k in-game currency for 5 premium currency). Nonetheless, it would be a compromise. How it would work is presumably up to the developers, but hopefully they'll make some wiggle-room in it so players who can't afford to buy the premium currency won't struggle with getting it in the first place.