Guess that depends on what a seastead is, along with the purpose of the design... As floating architecture, it can be stationary, or mobile. In my concept, it is free to move, for any number of reasons, with no notice. To move a city takes a level of preparation.
Increasing the mass of a structure unnecessarily, is wasted material and unnecessary expense for those wasted materials. In addition, those wasted materials decrease the buoyancy of the structure, further limiting the capacity, whether that requires a different design parameter, or reduces freeboard is up to the builder. Steel has more than triple the mass of an equivalent Basalt rebar, requiring triple the displacement, for an otherwise identical design, or reducing the carrying capacity.
Geopolymers and Basalt reinforcement have the potential to increase the buoyancy AND margin of safety, as well as the inherent ability to do a complete structural examination, rather than a visual inspection for obvious points of pending failure due to the inherent corrosion of steel within ferrocement and the inability to perform such structural examination. That lack of inspection and inherent corrosion is exactly why ferrocement has no realistic resale value, indicating an immediate loss of value and investment.
If you were buying such a composite structure and paying for the survey, would you want a simple visual inspection that cannot reveal anything about the structural integrity until it has reached the point of failure, or an identical appearing structure that has had a complete structural re-certification?