One Island per console limits the potential of this game, if they did not unlock this feature. It will affect the games playability lifecycle. (If one player) has lost interest on the single island. They will not touch it and no progress will happen on the island. If their is a feature of creating another island the player can try newer things without removing his/her old island and probably interact with his previous island. Trading with other island is another option. Possibles are endless.