Royal Caribbean is planning to follow Carnival's Fathom brand into Cuba, as early as late July, its CEO said at a press conference this week. He said the line is negotiating with Cuba and would move quickly if it gets permission.
One of the line's ships, Empress of the Seas, is coming back from a re-fit and has no cruises scheduled after mid-to-late July, and would probably be the ship that would be reassigned to Cuban trips once it completes those.
Since visits to Cuba by U.S. citizens require a purpose such as education, people-to-people activities, cultural exchange, etc. and can't be just for vacation, the line will either have to create a program, or limit sales to non-U.S cruisers, but there is no information on that yet.
Empress of the Seas (Royal Caribbean photo)