I believe Cunard (part of Carnival) operates the Queen Mary 2, the last running ocean liner on Earth. It does Southampton to New York via traditional Atlantic crossing, just like the Titanic (almost) did. Not sure if it makes money, but (pre-pandemic) it was likely subsidized by other cruise ships or by QM2 cruising herself.
It'd be cool to have a flight from Heathrow to JFK (?) on one 747 for people who want to experience the same plane. I think an airline enthusiast might go several times a year, and there's a goodly number of airline enthusiasts.
I think a flying boat tour of the Pacific islands would be a wicked honeymoon!