Adding voice chat will lower toxicity (story inside)
We all know League can be an incredibly toxic environment, and that not enough has been done to change that.
I play LoL with a college buddy of mine. We skype and hit the rift almost every day. He has other friends that he plays with and communicates with them over teamspeak. He used to have me on one line, and them on the other going at the same time while we all played.
Here is the thing though, I hated these other guys. They were better than I was, and they were obnoxious about it. We would be toxic to each other in chat and playing wasn't much fun with them. Till one day I joined their teamspeak. They were still better than me, but they could make call outs and give suggestions on the fly. Suddenly I found myself learning from them and the toxicity ended. Now we regularly play together and for the first time I carried a game they did poorly in.
The point is, when you can just type awful things it detaches you from the words. Nothing will be as good as having players sitting next to each other, but voice chat will be a big step. Please Riot, work on implementing VC for your player base.
As a side note, I can find no conceivable reason to have ALLCHAT in game. The only thing it does is cause players to tilt and rage and die while talking to the enemy team. If you need to report someone, mention it post game.