This would be so fun. They've managed to make vacation worlds and lots already and in previous games. Surely there is a way that it could be adapted for Sims to be able to go on cruises? 7, 10 or 14 nights.
I love the idea of weddings and let's not forget cruise ship entertainment, restaurants etc. And calling in to local towns. Id love a system like in TS2 where you can learn some of the culture like local greetings