My ideal world is one where the population of humanity exceeds 10trillion, but the population of earth is <100,000 permanent residents with yearly visitation from tourism etc exceeds 100million thanks to the series of space elevators that have been built. The majority of humanity are living in space at various Lagrange points in O’Neill cylinders and at least a quarter of humanity are in living in generation ships traveling to distant stars many that are >10pc away.
The Asteroid Belt has been mostly mined out though that isn’t much of a problem as fission/fusion generation supplementing the solar dyson ring has transformed us firmly into a type 1 civilization.