If I suddenly became a weird CEO billionaire, my vanity company would be "figure out how to cross oceans without CO2 emissions". Cool boats? Lighter-than-air travel? Some sort of ballistic passenger railgun? nothing's off the table
I did have the thought that "long" ocean voyages might be more palatable to people these days if you could guarantee internet access. Rather than the journey being part of your time off, you'd work remotely as the boat crossed the sea and your vacation would begin when you landed.
Basically put a coworking space on a ship. SeaWork. Done.
My gut feeling is that "make sea travel faster and zero-emission" is an easier target than the other two, just because no one has given much thought to passenger sea travel recently, it feels like. But obviously a better thing is social changes so that we don't really feel like we NEED to get across oceans in like a day, but can take our time. That really reduces the potential challenges! People used to be fine with a ten-day steamer journey across the Atlantic, until we got spoiled by planes.
I have done one big cross-ocean journey - I sailed on the Queen Mary 2 from New York to London. It took a week, but it was also a "cruise" - so you were there for fancy dinners, casino games, lots of food and alcohol, things like that. Like staying in a Vegas hotel for a week. That's fine, as far as it goes, but a week for one-way travel is a tough sell when you have limited vacation time. Also, it was expensive! It seems like there are different ways you could work that to make it a better experience.
I don't mind flying, but it's obvious we're going to have to give it up or lower the frequency that we take journeys that way, and the biggest blocker there seems to be crossing oceans. No real alternatives exist.
