Thought I would make this contribution to your thread. After the Concordia sinking - I reminisced about the one and only cruise I took with my sister on a Carnival ship. On board there was an elderly woman who was a ‘permanent’ passenger; she had determined that the access to medical staff, food and lodging was cheaper than assisted living on land.
Not as rare as I had believed.
http://notjustforseniors.blogspot.com/2009/10/cruise-ships-as-retirement-communities.html
My mom and I crossed the Pacific six times in the 1950s-1961 on Military Sea Transportation Service ships. Army troops on the bow and fan tail and military dependents in tiny staterooms stacked five deep in the mid section.
Two weeks at sea from Seattle to Yokohama. MSTS was slow but we had movies every afternoon in the day room and after dark, outdoors on the fan tail for the troops.
MSTS was the Army’s navy.