The thing with this type of reporting is that you need to be 100% sure that they will eventually break the rules. Since its in Champ Select you really have no proof that they are breaking the rules. People can say they will troll, or go to a certain lane, But once the game goes on they can play with the intention of winning. Dont get me wrong. There are clear cases when its plainly obvious the person is planning on trolling. But you need to see the bigger picture when it comes to something like this being implemented and how it could be abused.
I mean people already abuse the report function reporting people for things that are not reportable offenses. Also just to clarify what ARAM said off meta picks alone arent report/ban worthy. But off meat with the intention of feeding/losing the game is!