How To Get More People To Play Support!
In World of Warcraft (yes I know most will downvote this because they either think WoW is stupid or was good and went downhill), If you que for a dungeon and there aren't enough say healers going around at the moment, blizzard makes it so that if you que for that role you get a special benefit after the dungeon for being that role. I think this was a genius idea and although it isn't great in WoW, I believe it could be the key to success in LoL. If for example in ranked there weren't enough supports and that was causing everyone's que times to be incredibly long, Riot could make people who play support maybe get extra 3 LP at the end of the match (regardless of the outcome of the match). I know Riot and many others always say they don't want LP inflation, so maybe with the addition of Hextech Crafting, people who play the currently unpopular role could get a key/chest fragment or a key/chest guaranteed(depending on what Riot would want). Maybe they could get +50 RP or +150 IP or something similar. I believe this would be an amazing addition to LoL and would make que times so much faster and the overall game just better. Also, as soon as the amount of players playing X Role has evened out to about the same as the other roles, the rewards would no longer be available. The rewards could be adjusted based upon what Riot seems fit, either increased or decreased. Let me hear your thoughts on this as I think it would be one of the best additions to this game in a long time!
TL;DR : Add rewards to underplayed roles to encourage people to play them more. Will increase que times for everyone and give a bonus to those maybe sacrificing their happiness for others'.