Call me a pessimist but I think it is a mechanic that will be shoved down peoples throats, will earn many complaints and it will be revamped by constant patches till it gets plausible. And they made the mistake by having it start early (relevantly that is).
It worked on CiV 4, to have the UN because it was a late optional road and its resolutions (as far as I remember) were not going to make or brake the game. Now it seems once all CiVs are met are tied up to the rulings of the congress and more or less a Diplo victory race starts to unfold turn by turn. You are denied the option of been an Isolationist nation, you are denied the option of ignoring the congress, the prices by winning the various events are laughably (IMHO) one sided (to the winner got the spoils) and if you were bee-lining for another type of victory that involved, science or domination plans you are bound to be thrown penalties and have the constant threat of a diplo victory. Plus I cant see it working in multiplayer other than grinding runaways to a halt. In essence it gives the other civs the option to diplomatically gang on the runaway. Whether that is good or bad is subjective.
I can see CiVs that have gold or City-State abilities go up several tiers (Greece for example will be a major candidate for Victory it seems), and in MP the guy with the most city-states will effectively passing the rulings.
Yes you can buy votes, but realistically speaking, why should I sell you my vote and help you progress with your plans if I have a decent chance at victory?
The only dubious benefit I can see coming from this is the ganging up on the runaway but I wont hold my candle if it will be working thataway.
Sorry for the doomsday altitude but I just fear that the mechanics of these wont be as advertised. I really want to be proven wrong.
I don't think it works exactly like that in real life but I would trade unhappiness for the option of effectively rebuffing the council.