Further, the ruling is based on an interpretation of Congressional statute, not the Constitution. If American companies began moving their datacenters overseas en masse, Congress could just change the law.
What happens if an underwater volcano goes off one night, and the next morning there's a new island in international waters? Presumably there wouldn't be any guano to fall prey to the US Guano Islands act [1].
The rulings of international courts on such matters are irrelevant. Unless someone militarily stops them, or applies enough leverage elsewhere to convince them to stop, they will continue to build the islands and they continue to treat them as Chinese territory. The constant and aggressive American naval presence is the only thing stopping China from claiming the South China Sea as territorial waters.
Google building a island, claiming sovereignty, and hosting from there, as opposed to from some third country, would be without consequence regardless of whether their claim to sovereignty is deemed legitimate by some international court.
But maybe there's some Law of the Sea thing that makes that infeasible. (Not to mention the technical ridiculousness.)
Basically the case was - there was no way MS to comply with US laws without breaking Ireland's ones.
Also independent island could be turned into very dependent extremely fast by a team or two of Navy SEALs
The proper procedure here is to work through the State Department to get a warrant in Irish court. Presumably they didn't do that because they knew it would be futile, in light of Ireland's data protection laws.