IMHO, the idea isn’t about eternal structures, but the current commercial housing model is untenable, as is the current model of using steel, which corrodes and has a definite limited service life in a seawater (or even water) environment.
Even with my concepts, and the desire to use Basalt Rebar, and cement, or geopolymer cement, the goal is durability of the overall structure. I acknowledge the need for accessibility to the wiring, plumbing, and other sub-systems, as well as adaptability to remodel with technological advances.
Lambot’s original ferrocement boat is still serviceable. Several ferrocement hulls from WW1 and WW2 are still serviceable. I think that is a far more easily attainable and sustainable goal than build it, and scrap it every 25 years. It’s one thing to build in planned obsolescence, quite another to built for generational use.
My personal goal isn’t a floating city, but, rather, a floating homestead. If I get to build it, it will be built with the goal of inheritability. At 54, I know I won’t last forever, and I seriously doubt I’ll make any historical contributions that anyone other than my descendants will recognize. I’m not going to be building for everyone else. Doing for myself and my family is more important to me. Showing them that THEY are JUST as capable of achieving a lasting mark for their descendants is merely setting a bar to measure up against, and is the ultimate goal. The modern feel-good ‘I participated’, disposable achievement awards don’t make for that kind of impact. “My grandfather, great-grandfather built this and it’s worth keeping and maintaining” means more to me than all the hogwash about eternal longevity.
Use the best materials you can, make the best design you can.
Disposability is the current hallmark of human civilization. That is not something I want to emulate, or perpetuate.