Champion Mastery and Hextech
If riot needs ideas here is one if you own they should add shards into the accessories section and champions that you own already you can purchase buy there shards with IP depending on how much IP the champion cost that should be the amount of the shards and if they wanna make champion mastery and hextech more important by achieving mastery 6 and 7 they should give you skin shards for that champion that are not in the store or make it optional for you to in the store with RP for a certain amount of days or maybe give you an ICON for the champion and they can make a difference between purchased shards and loot box shards