It's been a long time since I proclaimed my basic Amtrak Faith here, but this is it: I believe there is an enormous pent-up demand for passenger rail, nationwide, both corridor and LD. (The LD trains should be thought of as overlapping multi-corridor trains.)
So I start with the assumption that in general, a goal for service should be two or more daily frequencies on every Amtrak route, corridors and long distance.
If we had service 7 days a week on the Cardinal and the Sunset Ltd, instead of 3 days a week as now, ridership on those routes would double.
We would double ridership on the LD routes if we had two trains a day each way on the Coast Starlight, the Empire Builder, the California Zephyr, the Southwest Chief, the Texas Eagle, the City of New Orleans, the Lake Shore Ltd, the Crescent, the Palmetto, and probably the Silver Star and Silver Meteor (tho they overlap and provide multiple frequencies for many miles already).
We could double or triple ridership on the Pennsylvanian, the Carolinian, the Adirondack, the Norfolk and Roanoke trains, as well as the Wolverines to Detroit, the Hiawathas to Milwaukee, the Hoosier States to Indianapolis, the Lincoln Service to St Louis, the River Runners Kansas City-St Louis, simply by doubling the number of trains on each route.
Not to forget the NEC. The Acelas now run hourly, and when the Aveilas come online in 2022 or so, they will run on the half hour -- but only during the morning and evening rush hours. If they ran on the half hour all during the day, I believe we'd still see full trains.
And not to mention the untapped markets like Scranton, Allentown-Bethlehem, Columbus, Louisville, Lexington, Nashville, Knoxville, Mobile, Baton Rouge, Shreveport, Tulsa, Wichita, Des Moines, Madison, Colorado Springs, Amarillo, Lubbock, and in South Texas Corpus Christi, McAllen, and Laredo, Among many, many others.
In short, Amtrak's potential to grow ridership far exceeds its risk of losing passengers due to demographic shifts. I'm just not gonna worry about that. I'll keep worrying about the need for another 2,000 or so new coaches etc. needed to satisfy demand.