We discussed some issues such a world will bring
here already.
Presently Outerra supports only spherical worlds, ringworlds would require several changes in multiple places, most notably a different geometry generator and new atmospheric simulation code. The shadow squares would be probably best simulated in the atmospheric code as well.
Terrain is derived from heightfield data that were processed into special format. This format can be also generated on the fly semi-randomly, effectively creating random planets. However, we are not following this path yet, because we'd be pedantic and it would take quite some time until it can generate planets that look realistic and believable. Our goal will be something in between - the ability to roughly sketch the planet, the continents, mountain ridges, land classes, and to have the generator producing everything else, including river network, volcanoes, mountains etc. It should be possible to hand place some features while leaving the others to the generator.