I have thought about this for a really long time, a little over a year now. As i see it, and as i have read about it, there are two ways to improve someone with bad behaviour. Either punishing or rewarding. I see that riot concentrate a lot on the first one, and really not much on the last one. I'll concentrate on the reward part as there is a lot of punishment already.
*TLDR: earn small amount of RP for behaving and winning, and lose RP for being toxic/AFK.*
What if for each winning game, each player would get not only LP as a reward, but also RP. I know that its one of the main ways riot earns money, but im not asking for much. For example, each time a player wins, the player gets 1 RP. You might ask, where is the improving part? Well, was thinking since riot is giving you 1 RP for each time you win and NOT behave badly, they can punish you when you get reported by taking away ie. 5 RP from you if one or more of your teammates reports you and the same if the enemy team does. For a total of -10 RP if one of each teams or all reports you. As for AFK, if they have been AFK for more than 10 mins, they get exactly -10 RP no matter what.
It is also possible to give -1 RP for each report of any kind. The exact amount of giving or taking RP is just an example, im sure riot can figure out better ideas. This way, the best behaved players will earn most which imo is something to look up for.
I have seen that riot have some sort of reward system for those who behaves, i was fortunate to get a mystery gift for free in january. This is really good, i never knew that. Only been playing for 2 years. However, i would rather earn and lose RP than getting a free mystery gift at the end of the season. Because winning and losing is more appealing than the idea that you might get a free mystery gift after a long, LONG year. Earning/losing RP is something you see each day and potentially each game.
Really hope for a consideration!