The idea of putting the players in charge of some piece of the setting is an interesting one, though one I haven't really explored. That doesn't mean that it's not on my list.
Back when I was running my megadungeon campaign, it was something that I knew was on the horizon. While it would be easy to assume that a megadungeon campaign would consist of "dungeons all the way down," the fact that I had lucked into recruiting an authentic Old School player meant that the idea of hitting "name level" was going to come with certain expectations. (One of the other issues with Old School play actually prevented this from coming to pass. Progression is really slow, so none of the characters made it to "name level" by the time everything fell apart.)But the idea of it stuck in my brain and is one of the big ideas of my current campaign. The map is blank and the world is new, so any nation that exists would have to be run by a PC. I'd go into depth, but I'm running a little behind. Maybe it'll come up later.