This just came across my mind as a suggestion for Urban Planescape. It might make a neat subplot in the history, perhaps as a source of some of the advanced technology.
In "Guide to the Ethereal Plane," one of the adventure seeds can be resolved by rescuing a dreamer who is sleeping in a stasis cell -- the only survivor of a technologically advanced ship full of colonists that crashed on a Mars-like planet several years ago. This would presumably have taken place before Faction War, as that's when the book was published, and certainly much of the entertainment value of the seed comes from having medieval magicians and planewalkers dealing with the airless environment and advanced technology of Ana's craft. (This planet can be reached since Anavaree, Ana's dreamscape, has traumatically ruptured and a path exists to the planet's surface from the Ethereal.)
So... what if we assume Ana was rescued? She has the mentality of a child in the dream, but is an adult woman and might be fully capable of dealing with high technology once awake (she has Int 10). As a colonist, she might have been a specialist in a mundane but useful profession, such as farming or construction. Keen adventurers might have, with her guidance, taken quite a bit of supplies and tools from her craft, possibly even loading a shuttle the colonists had and later using it as a base in the Ethereal. If the adventurers could reliably salvage a great deal of usable material with several trips, the use and spread of this stuff might have directed and spurred technological progress as people studied it.
Picture the following plot: Ana quite naturally grows close to her rescuers and marries one. The group and their descendants preserve the lost secrets of Ana's race, employing them when they have the opportunity, operating from their craft in the Deep Ethereal (which has since developed an entire orbiting constellation of stations). Occasionally, they release some technology through a front corporation when outsiders' technology has advanced far enough it can be passed off as simply a cutting-edge piece of work; sometimes they take "impossible" adventuring jobs, no questions allowed about methods. Both are quite lucrative. Anastasis Corp develops quite the reputation, as well as an air of mystery... and in the modern day has parleyed its experience with technology into a fine niche as a military-industrial conglomerate with a high-tech manufacturing wing and a mercenary wing, suitable as both a supplier and an employer for player characters.
By the way, Anastasis isn't just a pun on the words "Ana" and "stasis." It has connections to a primitive tongue (Greek in our world, possibly Elvish or Draconic in Planescape), meaning "to stand again," or "resurrection." Theologically, it also refers to the Harrowing of Hell. Ana was a NG NPC, and her rescue was the more morally upright of the possible resolutions to the scenario, so if this historical plot thread is followed, it suggests that her rescuers were good-aligned adventurers. Now, medieval warriors and magicians encountering high technology is fun in one way. How about a scientifically-minded scion of an advanced civilization encountering magic, and then angels and demons? The revelation that evil incarnate really did exist and, moreover, could be fought and killed... heady stuff for a materialist from a scientific world. Ana's descendents could well have a reputation not only as rich captains of industry and leaders of men, but as crusaders against the fiends and the evil denizens of the Ethereal and the elemental planes.
So, picture it. The party is on the Inner Planes, besieged. Soaring over the hill in their jetpacks comes a troop spitting lead at the besiegers, wearing recognizeable body armor: "It's Anastasis!" comes the cry. After their opponents are laid waste, the Corp mercs take them into the Ethereal, questioning them about the mysterious object they carry -- and, to the shock of the group, lead them to heavily-secured Colony Station, legendary heart of the Corp's operations. There, a member of the Family comes out to them, and explains that there's something even deeper going on...