A world-scale MMO city builder with depth that matches Cities: Skylines and with realistic supply chains for industry (ie, cargo traveling hundreds or thousands of miles) and realistic commutes (in C:S, a commute over 2 miles is likely going to be considered too long).

I just don't think a simulation on that scale can possibly work. Obviously, such a massive scale would have to be split over multiple servers, but I'd want the world to be seamless, as in, you can just pan over and see other people's cities. The player shouldn't be able to tell that the area they're looking at is being run on another server.

I just can't imagine how a system would operate. How do you perform path finding when the paths are likely to cross over areas run by a dozen other servers? How does it scan to millions of vehicles needing to find their path?