We probably have no idea how much demand are for a multiplayer CS.
I have no idea how much actual demand there is. Certainly not based on this forum. While there are those for and those against it on here, the people on here are a tiny part of all the C:S players, and likely not a representative part of the whole either. The only information that is available to me that I can use to make any sort of reasonable guess is that thus far, CO has not made nor made mention of a multiplayer mode.
I think many people imagine how great it would be. I can imagine it, and it's pretty awesome. However I don't think that imagination would match up that well with reality.
When I think of reality, I think of things like:
1. I spent 2 hours on my city, and now I can't work on it because my buddy isn't available. He's available next week, but I'm not.
2. Dude, stop putting your sewers upstream from my water pumps!
3. What do you mean it desynced and our last save was three hours ago!!?
4. Stop buying all the squares around me.
5. Actual conversation: "Should we connect our cities now?". "No." Then and hour of silence. "How about now?"
6. What do you mean you are building a wall around your city and you expect me to pay for it??