People think "multiplayer" = simcity
there is many aspects of multiplayer, not like adding someone to the region but try to get the ideas! think!
look at cities xl, they did just one little thing about multiplayer that was kind of cool after they actually fall off their first cities xl with monthly fees. They took their ideas to put it back into cities xl 2012 with the planet where you can actually choose your spot without going online!!
Multiplayer could be sporadic such as statistical data, or visual interpretation, to make you say "oh, my friend is in this continent, i can trade with him and make plane routes or ships route (transport tycoon fan here)
you don't need to add a "full multiplayer experience" you can just add a little tweak that will give you the sensation of having a cities among others. not like having a city on a squary map with no sight or whatsoever beyond it.
that is what cities xl succeded to do. you got your 10x10 km square, and then you can see the earth with your city on it, and say "oh great i can trade with "best friend city over there while im in there in the tropics"
Also "multiplayer" coud be ranged in one aspect, trade with the city you construct yourself! a feature which doesn't seem this game have!
it's like if you construct two cities, even in single player it would have been nice to trade with one another without going multi!! just this kind of idea people don't have! wouldn't have been nice to make cities yourself and trade tourism? oil? and stuffs?? you don't even scratch that idea!
i agree to have a solid base game, but i disagree of not pursueing the idea of something that can make a game enjoyable if it's thought right, and you guys have no imagination. (but maybe it's because im a game dev myself that i think beyond that, whatever...so let's keep the "lambda" idea, and be dumb to just stop at a sufficient level when you can reach higher layers.)