Hi Toby,
this is not really my Utopia but a scenario that might come about as a consequence of our actions, severe climate instability or extreme change, devastation of the environment and agricultural production making life above ground highly problematic. Its not that I want to go there but if we had to then we could make the best of it by learning all we can about how to survive come what may. Which also prepares us for other hostile environments on other Worlds.
The first sanctuaries are built to mitigate mass migrations, resulting from climate devastation, to prevent the destruction of the civilizations that lie in their path. It obviously is a monumental task that requires public support at a time when there may also be other environmental disasters, hardships, food and energy shortages or supply disruption. So there would have to be public information programmes to explain the necessity and gain support for them.
Following the success of the first sanctuaries more are built as a response to worsening climate conditions and the people adapt to the new ways of life. Populations have to be limited to the numbers that can be supported and social cohesion is important because the sanctuaries can not work as life support infrastructure and biosphere without the dedications of all of the people who make it all work. So there is also social engineering to ensure that there is a shared purpose, history, education and values and new measures of success.
The story is a vehicle for introducing a number of real problems and giving solutions. Somewhere in this discussion page there is a list of 14 problems that the essay addresses. I don't know if it is a complete list but those are what came to mind...population, child abuse/neglect, resource depletion, cancer, antibiotic resistance, climate change......
You wrote "Do you see a path that humanity should take to get to the destination you present?" Its a path we should not take but may be taking. Flavio Mercati has written "U-turn or U-die". I have offered an alternative to U-die,in the face of the unknown learn to survive in every way possible and survive. (Become good sailors.)
Thanks for reading the essay and for your comments and questions,
Georgina