Ability to select pre-1.9 or 1.9+ combat mechanics

Currently, many Minecraft combat servers use 1.8.9 combat due to the mechanics in 1.9 not being favorable to everyone. I would really like it if there should be an option when singleplayer worlds are created to use pre-1.9 combat mechanics or 1.9+ combat mechanics. This may be implemented through a gamerule or a toggle button when creating a world. Multiplayer servers should have an option to change this at the server administration level. This is when it would be more beneficial to use a gamerule instead.