On the subject of games that I would be running in an ideal world but never will, we just finished watching Man on Wire. (The life of a married man on a Saturday night in the biggest and most exciting city on earth, ah, glory days. At least I had a few G&Ts.) In case you don't know it, you should. In case you haven't seen it, do so immediately. It's the story of Philippe Petit, the man who in 1974 walked on a tightrope between the Twin Towers in New York.
The genius of Man on Wire is that it's presented almost like a Heist movie. Petit and his gang made scale models of the Twin Towers, sneaked inside on numerous occasions, made fake IDs for themselves, took aerial shots by helicopter, observed the comings and goings inside and outside the building for hours at a time. Because the event was technically a criminal act, it required meticulous planning. In the end it went off without a hitch.
So my never-to-be-played idea is this. The PCs are a bunch of thrill seekers, performance artists, extreme sportsmen and general glory hunters. (Rogues, if you will.) They exist to pull off heists just like Petit's, planning and executing daredevil stunts to impress onlookers, bring beauty to the world, pick up chicks and/or self-aggrandize. The cities and extreme environments of the world, from Tokyo to Everest, are their sandbox.
What the game would need to really make it work is two things:
1) Mechanics for making stunts at least a little tense. You can't get much more bathetic than a long drawn-out break-into-the-twin-towers sequence followed by "Roll 14 or more on a d20 to walk the wire."
2) Mechanics for garnering glory/attention or whatever you want to call it. What motivates the PCs in this game is accruing fame and attention, so there need to be awards which cover it, with mechanical effects in game. If you pull of a truly world-shattering stunt like the Twin Tower Wire, it will surely give you a boost in confidence and charisma and a warm glow which will have some sort of effect on future success or failure.
Some bastardized form of Risus with extra bells and whistles, maybe.