I've always loved the aesthetic of Steampunk. The problem is that I've never really been sure what the genre is supposed to be about.
Let me expand on that: Science Fiction is, for me, about examining issues of humanity, politics, sexuality etc. by taking them out of our context and placing them in another, very realistic and plausible one. Fantasy is about escapism - getting out of this world and exploring a better and more interesting one. Horror is about "the oldest and strongest emotion" and the adrenaline kick it gives you. But what is steampunk about, other than the certain visual style with which it is associated? Is it just a sub-genre of Fantasy or Science Fiction, or is it there to explore something else?
One idea is that Steampunk is about the fraught and nervous relationship between mankind and technology. New things are being created, but their very production and maintenance - the coal it wastes and pollution it produces - is debilitating for society as much as it works for the good. This neatly reflects our uncomfortable relationship with scientific progress, wherein new technologies create further problems for our culture and the environment.
In that respect Steampunk should be the genre of choice for a new supplement for 'legacy' games: as Gamma World was a way to play around with the world's crisis of the day (nuclear war), so a Steampunk game would be ideal for tapping into some form of zeitgeist or contemporary angst about environmental catastrophe. I can envisage a world in which the Industrial Revolution never stopped, and pollution-belching factories and vehicles ruined the atmosphere to such an extent that global warming has become frightening reality, with sea levels rising, desertification increasing and disappearance of animals. As land becomes scarcer wars and famine ravage the nations and societies collapse. And hey presto, Steampunk post-apocalypse is the result.
You could call it, "Carbon World".