To increase the amount of player interaction and overal increase the amount of fun+meaningfull battles there should be the possibility to have drop-in battles when you're facing someone in a campaign and afterwards the player who created the drop-in battle could be allowed to decide whether to use the result of that battle for the campaign (maybe add a difficulty switch for that) or play the battle again against AI. I think that would make for some awesome encounters, tactics and better fought battles.