No one will, unless it is profitable. I say that as a seasteader right now, I live on a boat.
There are a lot of ways to make money, as a tax haven, floating condos, convenience store (Marinea), tourism, exploration, etc. None of them are very profitable or compelling, because better alternatives already exist.
Tax free, Regulation free, manufacturing, could be extremely profitable. I guarantee the cost is at least 50% less than land based manufacturing. I am not sure if that is valid against China however, it depends on the labor component. That kind of cost savings will get investors to sit up and take notice.
Add in the additional benefit that the manufacturing can take place almost anywhere and there can be shipping savings too, not to mention the fact that If I was to build a boat in Tahiti or any nice location my wife would be much happier.
Once the floating Manufacturing niche has been realized, the gold rush will be on and a boom to rival China’s growth. A side effect will be cities surrounding the manufacturing centers.