Double combat system for future updates

So my suggesting to add in all the versions or add on the upcoming versions to have an option to choose between the two combat systems (1.8.9 and 1.9+). Currently a lot of people play on 1.8.9 because of the combat system being better. Making it so you can chose between the two would make a lot of people that prefer the old combat system (me) very happy because they would be able to enjoy all the new features without suffering from the combat system