Please don't think I am piling on, but my career was as both a Navy nuclear propulsion plant operator and then a radiation protection manager at a commercial nuclear power plant. I'm just offering some insights...
To answer the question: cruise ships will never be nuclear powered. Beyond the public perceptions by so many, there are more practical reasons for it not happening.
The costs for design and construction would be high enough to kill the idea, but the maintenance and operation costs would also be significantly higher than any increased operating costs as a result of oil price increases.
It takes a great deal of initial training and then refresher training to maintain a qualified staff of nuclear plant operators. A minimum of 2 years of training and you need a reactor simulator to do that at too. It is pretty much a standard requirement for SROs (senior reactor operators) to have a B.S. degree. Many of the other support positions require at least an A.S. degree. There is a pipeline of new people constantly being trained to fill vacancies in the Navy and at commercial reactor facilities - as people retire, quit, or their enlistments are over. The cruise lines would have to have a similar training program or risk having to remove a ship from service because they didin't have enough people qualified to staff the reactor plant.
A typical land-based reactor operator makes well above $100,000 a year, plus the support staff for chemistry, radiological protection, and maintenance, make almost as much. Multiply all those salaries by the number of people you'd need to staff around-the-clock shifts and you get into some serious money. You see, when you shut down a reactor you just can't walk away from it. It needs at least a handful of people sitting in the control room 24/7 as long as their is fuel in the core.
The ships would have to be licensed, which would be a problem since most are foreign-flagged and therefore the U.S. NRC wouldn't have oversight. Would anyone want to board a ship with a reactor approved by Liberia?
Ship-based reactors are small because they have more highly enriched cores than do commercial reactors. Think 'weapons grade uranium' here. The Navy didn't go to reactors on submarines and aircraft carriers for monetary savings. They did it for strategic and tactical reasons.
Commercial reactors are physically large and use fuel which only has 1 to 3% enrichment. They are more cost-effective because we can run them at 100% power 24/7 for an entire fuel cycle (18 to 24 months) before we have to shut down and refuel. That is a lot of coal or fuel oil equivalent.
Sorry for being so long-winded!