Good observation regarding retirees. In 1971 when Amtrak started up the critics explained that soon the old folks who remembered fine service would die off and then so would the demand for long-distance train travel. Instead, every year there were new retirees! And they wanted to go places.Trying to 'rebrand' service to fit millennials for LD trains is a fool's errand. LD trains inherently cannot depend on the business of people whose jobs provide, at best, two weeks annual vacation. We hardly ever took LD trains back when my husband and I were both working full-time jobs with limited vacation time--that time was simply too precious to spend several days of it on slow trains. The US is unique among industrialized countries in its norms of extremely limited paid vacation time, and businesses compound that by making it difficult to take even unpaid leave. So, depending on the trade of folks in their prime earning years is not a winning business model.
That leaves two classes of travelers for LD trains--one of which are people in rural areas not well-served, or in many cases served at all, by buses and planes. Those folks are the mainstay of LD coach travel, and with the continuing degradation of bus and plane service to fly-over country, I would presume that this market isn't going away in the post-pandemic future. The other class are those who ride the trains but have the luxury of having plenty of time for train travel--and yes, a lot of them are retirees. Somehow Amtrak seems to think that once they all die off, that group will disappear, but I would imagine that the next generation of retirees that replaces them would be a fertile market for LD train service--as long as the experience in the sleepers and dining cars is an attractive one. After all, the scenery and relaxation are not going away--and Amtrak has no way to degrade them!