Honor system should give an incremental increase to Lp gain at higher levels
One of the main issues with the old honor system that I think riot recognized was that a loading screen flair wasn't really much of an incentive. What better way to make people want to play honorably and friendly then giving a small boost to lp for climbing? It doesn't have to be a lot.
Honor looked like a 5-tier system. so how about a 1-lp boost at lvl 3, 2-lp boost and lvl 4, and 3-lp boost at lvl 5? I think giving friendly and honor players a path to climb the ladder faster is a great incentive and promotes good games in league without making it too unbalanced.