Hockey currently plays 4 on 4 in overtime. Why? Because it's easier to score. What do fans like more than fighting is scoring. I've heard suggestions to make the rinks bigger but this isn't economically feasible.
So some of the advantages of 4 on 4:
More goal scoring, therefore, more exciting games
Less injuries including concussions, since fewer players are on the ice
Lower ticket prices as the teams could drop 4 players each
Better quality play as with fewer players there will be better players
Now the one objection I hear is that the players won't allow it.