there is no way for riot to stop trolls
how could they do anything about it? lets do the math.
LoL has over 30 million accounts and milliions of games are played every day. if someone is reported in just 1 million games per day and it takes a riot employee 1 minute to review and judge each chat log, that would take 1 million minutes per day. that means riot would have to employ 2000 workers 8 hours a day seven days a week just to read all the chat logs.
even then they would have to review the behavior in the game. someone saying 'im going to troll and feed' is not a punishable offense. only actually trolling and feeding would be punishable. so then they would have to watch all those games and determine if the behavior is worth a ban. 1 million games per day.
it is just not possible. it cant ever happen.