I had something kinda like that in a Sci-Fi campaign that I never started... the Aether Drive.
I used a cosmology that was kind of a combination of Planescape, Spelljammer, and Myst. The basic cosmology was Planescape, but the Prime Material Plane had, between all of its worlds, the Star Fissure (instead of the Phlogistron (sp?)). The Star Fissure is a massive, dark void with a "breathable" atmosphere... there isn't really any atmosphere, but like the Ethereal Plane, any creature can breathe there, and all the primes are represented by glowing crystal spheres the size of a large planet.
By touching a crystal sphere, depending on the point you touched, and the angle your intersected it at, you could wind up anywhere in that prime's universe.
The Aether Drive was a small crystal sphere in the center of a Planeship. This sphere contained a tiny singularity that was regulated by a constant energy stream. While in a prime universe, the sphere would appear to be a window to the Star Fissure. If the stream's polarity was reversed, then the singularity would release, and the ship would fall into the Star Fissure. In this way, the ship's default location actually was the Star Fissure; it could only exist in a prime as long as the singularity was contained; if the power were to shut down, the ship would drop back into the Fissure.
Within the Star Fissure itself, the Aether Drive kept the ship "afloat", so it wouldn't be affected by the Fissure's ambient gravity (in the Fissure, everything falls. There is an up and a down... though nobody's really sure what's at either end. However, the worldspheres are unaffected by this gravity, and, if you're close enough to them, they have their own gravity, too. In this way, the ship is basically its own little artificial worldsphere), but when the polarity was reversed, the ship would simply fall into the worldsphere that it was orbiting... or just straight down. So, if you plot a proper course, you can "fall" into the worldsphere at whatever angle is necessary to get to where you need to be (assuming you've mapped the universe, or at least part of it). It was a pretty cool idea, but I never really went anywhere with it. I should think about that one....