I like the general concept, however, there is one thing I don't really like. Some champions, despite being "from" a certain region, do not have a City-State allegiance. They are what you'd call "free agents".
For example, Rammus. He was just random armadillo # 214532143 until he got zapped by some kind of wierd bolt of life magic in the Plague Jungles. Does he really have a city-state affiliation? Similarly, I think it's safe to assume that both Vayne and Lucian have "moved on" from their Demacian heritages. They would obviously still be willing to take part in events concerning their birthplaces, particularly since it, like them, stands for justice. But I can't say I would expect them to really have any sense of national pride. Another great point here would be Sivir. She, by all accounts, has no loyalty to anything beyond gold. How would she fit into any particular faction? Nami, Leona/Pant/Diana, the list goes on.
Bottom line, for this system to work, the affiliation of champions would have to be a lot more dynamic than it appears you propose in the other thread. You would have to build on the existing politics in the world, both to allow for the alliances in the Lore (Zaun/Noxus, Piltover/Bangle City), and also account for the champions that, while they may be from somewhere, don't really have a home in the political circles of Runeterra.