In-Game voting system
There needs to be an in-game voting system, much like the surrender, for someone on either team for being AFK or intentionally feeding the opposing team. I was recently in a game where our jungle Udyr got upset about something someone said in game so that player started running into enemy turrets and giving the other team kills. This was a ranked game.
This will give players in game more peace of mind that their 4v5 might turn into a loss prevented or the feeder on their team will get a loss while the rest of the team will get a loss prevented. The voting system should be viewable by both teams, with a majority of the total players agreeing that the player in question is actually a feeder/is AFK. This will prevent a team voting on one person just because they started loosing, and should encourage sportsmanship across both teams.
I know this is a team game, and sometimes you don't get the best teammates and you have to overcome that. That is just how the game works. But a 4v5 is a lack of a teammate, or an essential 6v4 with a feeder is not part of the fairness of the game. For a player to lose ranking because they got the feeder isn't fun for the whole team.
EDIT** This should be in place for RANKED GAMES (Solo Que) only.