(Posting this in a couple of places, just to see how different platforms handle it)
I'm a big fan of the Birthright setting that TSR put out back in the day. It hit a lot of notes I really liked - the world felt populated, politics had a powerful role, monsters felt mythic - it just rocked. But one subtle note always impressed me. In one of the nations of the game, the default one detailed in the core book, the High King's throne is empty. The main thrust of events revolves around the nobles and rulers jockeying to either seize it or to keep someone else from seizing it. There are several contenders, but no obvious winner. It turns out that was intentional - as the designer put it, the person they assumed would win the war for the throne would be one of the PCs.
I was reading through the recent Eberron Player's Guide and came across something that I found similarly appealing. One of the epic destinies in the book is the cleanser of the Mournlands (A nation destroyed by magic and now hidden under an unending shroud of magical fog). It explicitly lays out the character;s exit point from the game; the day they walk into the Mournlands and sacrifice their own life to lift the curse on it.
Now, there are other ways that curse might be lifted in a game - you could have a whole campaign about it - but that assumption that the solution is going to come from a PC is one that I find incredibly powerful, and is exactly what I like to see in a setting. Contrast this to the Forgotten Realms model, where we would know the name, race and class of the SUPER COOL NPC whose destiny it is to walk into the Mournlands and purify them, and if your PCs arereally lucky, you might be able to watch, or maybe even help a little.
I realize there's an appetite for both of these approaches in gaming. Some players would rather be the audience to the world than the main stage, and that's fine, but I think they have historically been overrepresented in published settings, and it's always nice to see a little strike against that approach