Cruise ships are essentially floating luxury hotels. They are utterly dependent on supplies from port and on labor that is segregated from paying clientele. The base unit of seasteading has to be more self-sufficient. It has to supply food, potable water, and shelter for at least one permanent resident, plus many more transients to realize any economies of scale.

The ship has to be able to never make port, because all ports are potentially controlled by potentially unfriendly government regimes, and defended by armed navies. The ideal of a seastead is to live indefinitely on the high seas, outside the jurisdiction or interference of any nation, as an unflagged vessel.

But the stride from here to there is so long that even Jean Claude van Damme would pull a groin muscle trying to make it in one step.

Operating a retrofitted extended-stay cruise ship under the flag of a disinterested landlocked nation would provide very valuable maritime experience. Even Carnival Cruise Lines, a company specializing in cruise operations, has had some trouble operating regular cruises. I can only imagine the sort of unmitigated disaster these guys could brew up if given enough cash.

Keeping a ship afloat at sea is not as easy as everyone seems to think. I'd like to see these guys keep a regular ship out of Davy Jones's locker, running experiments and proving concepts for a few years before I'd find them credible operators of colossal floating concrete platforms.

Presumably because cruise ships aren't meant to provide any sort of sustainability, like farming, and requires fuel.

Sure, but you have to start somewhere. If people can't deal with operating a cruise ship then I question their ability to create brand new floating islands and run them sustainably. Surely one could do some farming on a cruise ship (using a mix of decks and hydroponics) and likewise generate some energy on-board. Obviously not as attractive as running a small nuclear power plant but you probably can't buy a used nuclear aircraft carrier, so you're stuck with diesel in the short term.

I think with the same costs that go into a cruise ship one might implement a more optimized platform for farming.

If you're commissioning a new cruise ship perhaps. You can buy a few second hand cruise ships for a fraction of that cost.

Farming on those is even more absurd -- take the most land-extensive activity and build an insanely costly small platform to perform it!

I wonder if it's possible to connect a bunch of modified cruise ships in a sea colony. That would make it readily expandable and modular, plus allowing enough space for all kinds of alternative energy/food sources

Cruise ships are designed to return to port every week or so to restock supplies.

You need something that can easily be restocked at sea.