Remarkably well, I'd bet. The person you were quoting didn't have quite the correct math; the number of road segments for N cities does not go as N^2, it's closer to going as N. Often you'll have a single transportation trunk line going through your main cities, with only short spurs going off to the side cities. But regardless, think of it this way: if you're packing your cities in, then regardless of geometry, each city would be about 4-5 hexes away from its neighbors; less means overlap, more means unused tiles. So no matter how many cities you had, connecting a new city to the network would cost 4-5 tiles' worth of upkeep.
The only question would be how well the AI would do this, but it seems to be doing a pretty good job so far.
I wasn't talking about the road analysis (didn't really read it), I meant how would humans react to AIs being asshats and ganking all of their food? As well as the question of making the AI competent enough to actually do that.
But again, I think the underlying problem with the happiness system is that it isn't adjustable. If you know there's going to be a 5-turn period of extreme unhappiness before your new Colosseum is built, you often have no choice but to just wait it out. There's not an easy way to temporarily boost happiness at the cost of science or production. That's why I'd like to see the Entertainer/Empath type specialists implemented.
You are getting dangerously close to slider territory, here. The massive reduction in short-term fungibility of resources from previous games is a good thing, IMO.