This is probably better suited for the 'Suggestions' forum, and I don't even know that MP is on the roadmap for Rimworld at all, but I would be very much in support of your first idea.
The second I could see being a little more problematic, you'd need to perhaps split 'ownership' of the population with each player's population prioritising first their own player's priorities and plans before assisting the other players.
The second I could see being a little more problematic, you'd need to perhaps split 'ownership' of the population with each player's population prioritising first their own player's priorities and plans before assisting the other players.