There are three things I wish Riot would fix...
First, the Chests and Keys. (Not the system itself, but how you get the keys and chests.)
The system is fine, you have to work hard and try and score a S on any Champion to get a chest... but why do this as well for the keys? Why must my teammate(s) have to get an A as well just so I can get a key shard that needs to be done 3 separate times in order to work?
I believe that there should be a reward that grants you a key shard for doing a first win of the day that goes along side the IP bonus you would get. And if you do this 6 days in a row, the seventh day should reward you with a chest. This would mean a possible extra 52 chests a year (at most) but I believe this would go towards a more fun rewarding system that challenges the player(s) to keep going and not feel as if getting a chest or key is too difficult.
I also wish that instead of waiting a year for a champion to be available to unlock a chest again, that it should be just half a year. Half a years time is a lot when you come to think of it, the sudden change from Summer to Winter, Fall to Spring, and vice versa. Its a long wait, and these are the champions the player might main and have fun playing with. There's probably little chance someone is going to be able to unlock a chest from all 130+ champions and even if they did, that's probably just 1 out of around 50 players on this game (so if its a million, that just 20,000 out of a million players who probably already own all the skins and just want to try and do the feat).
Also, if we could it would be amazing to transfer old champion points into the other points. It can be a crazy number like 2,500 Champion Points = 1 Point. So even if you had a million Champion Points, it would only equal to 400 Points in total which isn't too terribly much. But its also fair since you had to try so hard to get so many chests just to accumulate a ton of Champion Points in the first place.
Second, I wish that Twisted Treeline would get a remodeled map... not that its a bad map, but like the old Summoner's Rift it would be nice if it got some love.
And third, I wish that Showdown came back as a permanent game mode and following it was Butcher's Bridge as it was a 1 v 1 ARAM match (or a 2 v 2 ARAM match). Since its based off of Howling Abyss, it should still be a ARAM esc game mode.
Sorry if this is just selfish...