Nevis (the baseball) was only boat accessible, and St. Kitts (the bat) is mostly hills of national park.
Vast majority of things must be flown or shipped in. I am hard pressed to see some "techno libertarians" doing techno without Amazon/Temu/Walmart/<insert fav vendor> in 24h drop ship.
I think this is an unreasonable bar. All the fertile land in the world has been accounted for. There's no way to accomplish that type of sustainability without conquering existing land or some major technological breakthrough.
I think a fair bar would be economic sustainability. Plenty of countries depend on trade for food, but can make up for it in exports.
What is your definition of "techno libertarians"? asking because my understanding is that their primary work and concentration of work is not agriculture; there is no need for "fertile land". They can build stuff on a rock like Hong Kong.
I image this as a bunch of F/LOSS techno peeps living in condos or town homes with postage stamp grass to take care of. they would run off to the shore to do some water activities, go into the town and do some restaurants and some such.
Basically, this reads like an attempt to anchor digital nomads.