"make long distance travel slower and more digestable, like a cruise ship on land."

I don't see how that would work. Cruise ships are an enduring business model because even when they're not at in a port, they have the necessary space for tons of amenities to keep guests entertained.

You could never fit anything comparable on a train or a bus. Not without creating some sort of lumbering land-behemoth that would end up producing more greenhouse gases than it would save.