have like  relationship system which lets you combine if the 2 systems are close to each other,    like a marriage system, so they can combine their force and work as a team, the systems and the ships they control become one and they both work with the same things, also if the brake apart then the on which wants to brake apart looses more the the one who don't (if they brake away the one who wanted to brake away gets 40% of their shared system and the one who didn't gets 60% of their shared systems) . if they win then the 2 players win but they would have to reach 70% more score to win. e.g. if the normal score is 100 to win then they would need to get 170 to win.  there can only be 2 in this type of a relationship,  i think using this type of ideas will bring more dynamic to the game with more options for the players to choose from making the game feel endless not only in space by in the thing they can do.