The idea is interesting but it seems to underestimate the amount of resources that ships and platforms take up. The maintenance costs are just massive. They require continual work and parts replacements. The sea is a very harsh environment. There is constant buffeting by water and the salt and moisture causes corrosion and if one is not very careful growth of mildew and other nasties. There's an analysis commissioned by some of the seasteading people here which is worth reading but I think that it is very optimistic about costs.
These are certainly difficult problems, but they are all solvable if just enough money and expertise is thrown at them. The cost would be very high, but the potential profits in the hypothetical case of success (i.e. establishing a functional seastead with de facto full sovereignty) are vastly higher. I don't think any technical problems are comparable to the political issues involved.
Recently the relatively awesome entrepreneur invested 1.25 million USD into this (seasteading institute website here).
It seems such a wonderful concept, finally somewhere where new forms of government could be tried out. But I'm just wondering how in the world they hope to deal with existing governments since their reaction to any kind of serious alternatives, especially one that either economically or ideologically presented a significant challenge, is bound to not be positive.
I was just wondering what LWer thoughts are on this matter? Also has there been any discussion of seasteading in the past that I've missed? Also I'm wondering if anyone would hazard to perhaps offer a prediction or judge how likley this is to succeed (maybe on predictionbook)?