Some ideas

About the loading screen borders, if they are there to show your rank, why not show it to everyone? I get the idea, but if people can't find out about it in-game they can just use any website that provides this info and will ultimately check what could be checked in a second. At least change it for normal games?

An in-game feature to list all skins available in the account, as part of the "Collection" tab.

Ever thought about a ranked queue for ARAM? No, really, knowing how to play and win with a random champ and comp doesn't seem like a bad idea, at least for me :P (maybe with a few tweaks like free shopping?)