I'm still only playing single player, but I have a suggestion. I don't believe it is implemented. 


What about hotjoining multiplayer? In other words, players can play 'single' games by themselves which are open to others to join midgame. They take over by an AI and if they leave the AI takes over again. Of course, this would merely be an option someone can enable or disable. 


Usually grand strategy multiplayer games are incredibly long. This feature would make it easier for people to experience multiplayer, at least to some degree.