There are survivalists who would like a home that could have a good chance of surviving various potential disasters like breakdown of society, nuclear war, disease outbreaks, etc. A survivalist seastead is a Single Family Seastead with the features of a Self sufficient seastead and a few more issues. The additional issues are below.
A seastead could stay isolated from other human or animal contact to stay safe during a contagious diseases outbreak.
A ham radio with PSK31 would allow communications at typing speed for thousands of miles using a low power radio (like 20 watts). So keeping in contact with friendly seasteads would be possible.
A survivalist on a seastead out in the deep ocean sort of has a big moat around him making attack from hungry people trying to get the survivalists food less of a problem. In a post apocalyptic scenario the number of people that could still travel across the deep ocean and be a threat to a seastead would be much smaller than the number of people on land. People with sail or solar powered vessels are probably fishing and not so desperate to steal food as land based people would be. Also, with radar or other sensors you can see a threat coming when it is still far away. Defending against a pirate attack that you see coming should work well. Most pirates seem to break off an attack if there are any guns firing at them.
A usual survivalist shelter is an air-raid shelter. An attacker could get very close without being seen. If they make a smoky fire by the air-intake for the shelter the people inside can be killed. Then they can break the door and take the food. So a typical shelter may not really be nearly as defensible as a seastead.
Survivalists often want a fallout shelter. Being on the ocean there should be much less risk of being near a nuclear bomb detonation as they will be targeting land locations. If there is ocean for thousands of miles upwind of your location then the odds of getting fallout is greatly reduced. Also, on the ocean it is easy enough to wash down any surface that might collect fallout. And any fallout on the ocean near you gets shielded by the water it is in (and probably settles down to the bottom). So even if a seastead did not have a shielded room it is still probably better off than a land based shelter.
A seastead could have a room that was below water and so shielded from radiation. This is probably not necessary. Might have a room where water tanks and food storage was around it to provide some shielding.
Many survivalists want to have a retreat or bug-out-location. This should have plenty of water, be in a low population area, have good solar exposure, far from population centers, not downwind of major targets, and defendable. A seastead fits these goals well. In addition it is movable. So a survivalist could get onto his seastead when he thought things were going bad and set out to ocean. If he is leaving in a downwind direction (say from California) then he would want more than 1 day lead for a nuclear attack, but that is only one type of problem.
It is not clear how many survivalists would be interested in buying a seastead. This would depend on how much seasteads costs. But even a small market segment could help with initial sales of seasteads.
A seastead can be a great platform for a survivalist. It can be equipped such that a family could live for years without needing any resupply of any kind. It is probably a more secure situation than a land based home where hungry people may attack at any time. Seasteads should appeal to survivalists.