examples from the real world
I was thinking, in one of my less lucid moments (or maybe it was more lucid, but regardless) of a way to ensure that everyone participated in, or at least had an interest in, some sort of PvP area that could be controlled by either side. I drew on the real world example of mobile phones. Mobile phones use an ultra rare ingredient called Coltan that can be found in only a few places around the world. Since mobile phone production is so important, securing coltan has led in some cases to a real-world PvP sort of situation.
Once I had a real world crazy example, I thought 'why not get really crazy' and base the game on RMT, with currency having both a buy and sell rate (with a commission earned by the game maker in both directions).
Assuming you make the game fun enough in all other respects (big assumption, I know), this in-game element could become as contentious as the real-world example I drew from. Since we already know large organizations get involved whenever there is money to be made, one can imagine the whole thing blowing up into serious RL drama.
Obviously, this is all a thought exercise, as I don't think, in the end, this would make for a stable game play experience, but it is interesting (for me, at least) to think about ways in which the real world could be drawn into the game, giving the game a richer background.
I have the impression that Eve Online may live on the fringes of this sort of thing, but I need my games a lot more carebear, so I'm not sure.