I'm also interested in reusable forms for dome home construction. I also would be interested in an engineered design for a home that could be replicated to help spread the cost of design. The cast in place textured ceiling would be awesome!
Aquarist here - cement is not considered safe for fish, the lime content is too alkaline for them. I don't think it would be recommended to hold water for human consumption, either. There are lots of options for that including water bladders and plastic bins and towers of all sizes and shapes. If you don't want to use a liner for a pond (containing fish life) you can use a clay base to hold water in fairly well. It will seal better over time as the fish add to the bottom layer with their excretions.
Interesting points, however I would offer that Hawaii has MANY microclimates depending on island, and Big Island is probably the most diverse. The relocation to Hilo is just about 20 minutes from a rainforest where I happen to have property, and there is NO sandy soil. I believe they are located in Hilo which is MUCH warmer and sunnier. Sounds like both Hawaii Island and Puerto Rico both need solutions for low-resourced communities, but certainly if a workshop is offered in PR, I'd consider visiting!