Hmm Mastery skins/Mastery reward

Well this is usually a topic most people don't like cause its basically free skins u get as reward.. but What about mastery skins which are advanced versions of the champions? Like for instance.. I got the idea while looking at ekko, and his could be like.. at mastery 7.. Unlock the more technologically advanced Adult Ekko ? .. Not every champion would have an adult skin cause most are already adults so I thought the skins would be like Elite (Champion name) or something.. maybe like Elite Xin Zhao.. where his skin would be him where he's old and wise enough to teach students.. would have like gray hair and battle scars etc. or for teemo.. an older teemo that has like a combat scared past and is wiser and less cute. This would be somewhat hard to workout for champions from void or the isles, but I think instead of older or more experienced, They'd look more vicious and threatening.. like Thresh would have some more spike based armor and his soul flames would have edges and actually come out of his body like particle effects.. or koggy could have an evolved state or look more refined etc. Just something so people that get that high are rewarded.... Or maybe make like a system for rewarding champion kills or champion mastery or something. I dunno I just thought of this out of nowhere and thought it would be a cool and nice feeling for those who put a lot of experience into their champions [galio-happy]