If I were running Amtrak and confronted with this dissatisfaction of solo travelers with having to deal with seatmates, I would want to first find out how many people are affected. In other words, is this a big potential new market or just a few loud voices? When I ride coach solo, I usually have no problem with seatmates, even when I'm forced to have one. And, I've never had to have a seatmate for a whole long ride. This may or may not be a problem.
It does seem to me that a premium coach or "business class" product would be worth offering. The ridership and revenue figures posted by RPA for the various long-distance services show that those that offer business class get a revenue per passenger mile similar to what they get from sleeper passengers. However, this is achieved at a lower cost, as they don't pay for attendants and meals, and they can fit more of these premium-fare passengers into a single car than fit into a sleeper. In other words, it could be a great cash cow for the Amtrak long-distance services, just as premium economy apparently is for the airlines.
However, I think the seating should be 2-1, as (1) this allows more capacity for the car and thus has more potential for selling premium tickets, and (2) couples and families also might want to ride this premium coach, and they might prefer to sit together with their traveling companions. The premium service should allow seat selection at purchase (or right after purchase, if that's the way the reservation software now rolls). This shouldn't be a problem, as Amtrak is doing it quite well with the Acela and Northeast Regional Business Class. Heck, there's probably no reason why they can't allow for customer selection of sleeping car rooms and coach seats as well. It might solve a lot of problems and reduce on-board friction during the trip.
