My problem with this is the potential for exploitation. Players can use multiple characters in a game to get an edge over their opponents. Currently, it's not a game breaking issue since all those characters have to work independently. Sure they can trade together and even gang up in successive attacks on another player, but each individual attack is on level ground, both fleets built by characters with the same amount of time to grow and collect resources. Allowing players to formally gang up in fleets, etc. could potentially throw that balance off much further and make it a game of who's got the most characters.