[Suggestion] Have your end game rating influence LP gain/loss
To clarify, I'm referring to your end game mastery score (S, A, B, etc). I think having this would reduce ragers/quiters, as their performance determines their final LP gain/loss (hopefully making them more willing to continue playing in a losing game).
It'd also be nice to be recognized for your performance.
E.g. If you feed the enemy, but you still win game, you probably don't deserve to gain the same amount of LP as the person who carried you. Or if you play really well but end up losing, you don't deserve to lose the same amount of LP as your feeding teammate.