So simply "sailing under a flag" gets you quite a lot of the potential benefit of seasteading. Sailing without a flag is something to think about in the far distant future but not really worth worrying about for now.
There are oodles of business models that could make use of this today. Right now, the only one that's really been tried is "day gambling cruise" - sail out of a port where gambling is illegal, gamble once outside the relevant imaginary lines, sail back into port. But there's lots of other business-space to explore, like medical cruises.
Currently many Americans fly to Germany to get medical operations that aren't yet approved here or fly to India to get medical care that is far less expensive than here. Those who live near a port city might save money and time accomplishing the same end - cheaper, more flexible care - by shuttling out to an offshore floating hospital.