Setup to switch Combat mode : to pvp 1.9 or 1.8 or new combat update

hello my idea is to be able to switch the combat mode to 1.8 or 1.9 it will not be a gamerule but a mode that we choose in the menu settings when you want to create a world and be able to do it on the serveur config like that people who want to play in the new update but he is disgusted by pvp 1.9 can play on pvp 1.8 and people will finally stop bitching the game about the combat update systeme since they will be able to choose the combat mechanics they like.