I'm going to be a bit grumpy for a moment: it's really annoying when people (in this case, the author of the Railway Age article) assume a generation will all of a sudden change and become just like other generations "when they get older." That isn't known, and it comes across as though this person knows better than the lived experience of the generation that they're talking about.
That aside, if we look at what changes are happening in the dining-out world (at least pre-COVID,) the biggest change is that people are fine with counter service and bringing food back to their own table, but still expect high-quality food. In fact, if anything the standard for what food is served is higher than what it was before, especially on the lower and mid-range levels. As but one example, Chipotle is popular because the food is made fresh in store, they at least advertise sourcing high-quality food, and it tastes as though it was made relatively fresh and specifically for you (with it having the toppings that you want.) While having a full Chipotle (or similar) line may not be practical on a train, bringing back a chef to make high-quality meals fresh on board would be a huge improvement that would actually reflect what practically every generation wants. Cost savings could still be found by doing counter service to order and pick up the meal, with the counter attendant offering to bring the meal to your table if need be. Dining car space could be self-service, perhaps with some signage to indicate whether a table is open to meet new people or is wanting to eat their meal on their own. For some people this may not be ideal, but I think most would still find this acceptable and, given the cost savings over full diner service, would still be far preferable over the current options or other potential experiments with dining service in the name of saving money.