If the ship is always docked, it has less appeal, I'd love to live in one that keeps moving between ports, even if it never goes much further.

In that case, power is an issue. We'd need a powerplant that's green (because cruise ships are anything but - at best carbon neutral). The only reasonable choice I see would be small nuclear plants and that's something that hasn't been attempted with passengers since the NS Savannah. If that is solved, then I'd love to move to one.