Skin Loans via Mastery Tokens

How about:

After reaching mastery 7, earning an S in a ranked game rewards you with a skin lending pass which allows you to lend a skin to a friend/Ally for one game. This could conceivably be used by a player to incentivize allies to play a champ that they want them to play. Perhaps the lending should be limited to the skins for the champ the S was earned on.

Bonus round: A new Prestige chroma that can only be used by expenditure of Mastery token.****