I agree with quite a few people here. basically, in a nutshell, co-op should work with factions and races possibly…Races would determine your settlements race, obviously. and Factions would determine what “team” you are on. Depending on what Faction you are on, you start on a different area of the map, with different resources, monsters, etc.
Player 1: Race: Human - Faction: Blue
Player 2: Race: Orc - Faction: Blue
Both Players will have control over their own settlers and what they build or what they do. Player 1 decides it wants to be a farmer and a medic because that’s his favorite thing to do in the game. Player 2, being the of the Orcish race, decides he wants to be the main controller of building defenses and fighting.
Obviously there is going to be a lot more to the game than fighting, building and farming, but basically you cooperate with one another to create the most successful settlement possible.
Perhaps each race has a different building style, or different strengths. When an orc builds a guard tower on the edge of town it has bones and spikes protruding individual types of blocks making it look formidable…
Or perhaps the humans contribute to the settlement by offering healthier crops and/or helping the fighters by keeping their health higher than a different race would.
Maybe the “host” of the game should be able to choose whether or not different factions should be able to play on a certain server and if PvP should be allowed, or perhaps the host should be able to choose the difficulty and quantity of monsters on the map so that players co-operating should have to work harder and make better defenses to survive.