Hello Georgina,
I've quickly read your essay once, and I find it quite original and entertaining. Your style of presentation is cute.
At a quick glance, there are two aspects in your described potential future that do not look too attractive to me.
The first is that there appears to be a clear separation, even more marked than now, between the good inhabitants of the sanctuaries, and the criminals, terrorists and debris (that pose a threat to the ventilation shafts and logistics portals, or threaten exchange mission among sanctuaries).
The second, in part related, is the overall impression that the life in the sanctuary system is based on regulations imposed from above by some authority hidden behind the scenes. Because your text is very suggestive, even visually, it may be that it has induced in my imagination some unintended resonance with some common place science fiction scenarios, as seen in some science fiction movie (does `Zardoz` ring a bell?), or read in some book.
Nevertheless, I wonder (i) whether you feel that any future stage of humanity will unavoidably have to cope with a percentage of bad guys, and, perhaps less naively, (ii) how you imagine the transition from our present world to the sanctuary system could take place (e.g., whether peacefully or not).
Tommaso
PS1. Humans are becoming symbiotic residents of living man made hosts. Sometimes, when queuing in my car along the highway, I feel we have already got to that point.
PS2. I see you have a lot of comments above, which I could not read. If you feel my points are already covered in some previous post, let me know, and I might stick in at the right place.