[Mysterious Dark Lord v3.2]

Ringworlds do depend on rubber physics (or at least unobtanium, which is what scrith is). A more realistic distant future megastructure would be the Grand Array (seen occasionally in the stories of Jonni Future published by ABC Comics - mediocre stories but the setting is full of potential).

The Grand Array is a Type-I Dyson Sphere - i.e. the planets dismantled to make several trillions of space habitats of all kinds orbiting the sun at a variety of distances. From the outside, the sun would be completely dark as all of the stations absord the solar energy. In this way, all of the sun's energy is accesible by local civilizations and the habitable area of the solar system increases by a factor of billions.

Such a megastructure does not depend on rubber physics at all, merely godlike engineering skills to dismantle the planets. Millions of civilizations of all kinds can co-exist without even knowing of each other's existence.