The problems with OPC are multiple, from a practical point of view. For one, if using an iron based armature and components, such as a ferro-cement type hull, there will be Chlorine ion infiltration, in seawater, eventually leading to corrosion., another is bi-metallic corrosion, which can even be caused by making an electrical shore connection, in a marina. A third would be the potential loss of integrity, if there is a fire. if we are planning to build for centuries, rather than creating things that may last a couple hundred years, then we need to use the best materials available, not just the same old stuff that has failed to create permanent infrastructure. Just look at the reports of failed bridges and buildings, due to the internal corrosion of their steel armatures, as well as the acknowledged probability that, in the US, alone, it is estimated that 70,000+ of such existing structures are ready to fail.
The nice thing about the known chemistry of geopolymers, is that they are so Basic (High numeric pH value), as to prevent the corrosion, by inhibiting the infiltration of the ions, so long as there is structural integrity. Add that, in cases of repairs, OPC is difficult, at best, to get to adhere to cured OPC, while it has been demonstrated that geopolymers will bind to existing cured geopolymers with nearly the same strength as the original material, before the damage occurred.
Add that, by eliminating high concentrations of Calcium, geopolymers become mostly X-ray transparent, allowing for existing field technology to provide a complete examination of internal structure, for inspection purposes.