Big Ships can be VERY FAST with today's propulsion. Even a Panamax ship -- one that is smaller than the one you designed will have a hull speed of 42 knots with a traditional displacement hull. With wave piercing designs you can get close to 50 knots, all without exponentially large increases in installed power per ton. That is twice as fast as the typical cruise ship. So speed exceeding the United States' is very attainable. Cruise ships however does not really need to have the bad weather, year round atlantic cross capabilities of oceanliners of yore whose major function is transportation in form of a scheduled service between two points. They move around throughout the year looking for fair weather and pleasurable seasons.
I have to disagree
plate friction of a ship is 0.5.*ρ*V^2*wet surface*Cf. the V is the speed, Cf is the form factor given by reference ships (ITTC 75, for example, is common.)
if we asume the ship stays withing hull speed, we can assume the wave resistance grows with the plate friction. it does not, it is exponential, but we can assumee it does.
the wet surface and the shape stay roughly the same (let's assume that too) and the ships stays in water, so the ρ stays the same too.
now, with the above, we can see that when we make V (speed) 2 times as big, the resistance gets 4 times as big. power is F(resistance) * V so the required engine power gets 8 times as big. I would that call an exponentially large increase in installed power per ton. added wave resistance can make matters worse even.
while modern technology allows ships to go faster then the fast liners of old, there is a cost for that, and with the aircraft as an always faster alternative, I do not know if this is worth it.
then, the wave piercing bow. the reason why people chose the ship over the plane sometimes is often comfort and luxury. as a wave piercing design decreases seakeeping and lessens usable space and weight on board, I do not see why an wave piercing bow ever being an potential on cruise liners.
I also disagree with your saying that cruise ships do not need all weather capabilities. cruise ships often sail in lines too, but with more then just 2-3-4 harbours to enter. they have a schedule too, and are expected to keep it. while modern cruise ships often do not have good bad weather characteristics, it is not a bad thing to say they should have and decreasing their seakeeping from the current designs is something that will not happen. pleasure yachts, on the other hand, stay in port when the weather is bad, and do have decreased seakeeping ability (that is, when their owners are on board, the crew is often expected to move the yacht from one place to another trough bad weather)