I think it depends partly on the type of seastead. Those of us looking for a laid back rum drinking life in the Bahamas won't necessarily want a super fast way to Miami & vice-versa. Also, that would run through a little obstacle known as the Gulf Stream. For those of you who don't know about it, it's a pretty strong current pushing north between Florida and the Bahamas. That much pressure on a tube running between a floating seastead and land wouldn't be ideal. For a economic powerhouse seastead with the money to connect a ridiculously expensive subway tube to shore, go ahead. For now, this should probably be in "Wild Ideas." We need to focus on getting something up first, then we can worry about fancy gadgets. And who would want to invest in connecting a hyperloop between Miami and a pilot project? If the pilot isn't economically viable, this ain't happening for sure.
Also Matias, the problem with a rogue wave is that they are unpredictable. We can't say "Oh, there will be a rogue wave today, don't ride the subway."