Honestly, I wasn't terribly impressed with the "Full Service" dining options to begin with. I miss the Signature Steak, but even that was about on par with what you'd find as the special at B-grade truck stop restaurant. There a lot they could do to enhance the overall experience, even assuming an on-board chef is never going to come back AND realizing that the train fan demographic has been decimated by COVID.
1) Eliminate the paperwork: Give the SCAs and Dining Car Attendants mobile devices to allow them to take orders, know which passengers have meals that have been ordered in advance, confirm service times, give reminders of when dinner items should be picked up, passengers checked in on, etc...and otherwise respond to passenger requests.
2) Better plating: Right now, "Flex Dining" is TV Dinners with a salad and sometimes a roll. Just as Flight Attendants or European Cafe Car attendants do, the staff can heat up different portions of a meal and serve them on actual plates or prepare a tray. I'm assuming they were already doing some version of this with the "Full Service" dining, but the plates and silverware tended to be all plastic.
3) Reusable Tableware: Get rid of the plastic. Reheat items in foil which can be recycled. Use plates and silverware. Airlines have trays and other systems for washing these items off the train, and with a little imagination Amtrak can cut down on a lot of waste and provide a better experience.
4) Local options: When going through Denver, I just order Postmates/Grubhub and pick up by dinner on the 6 (or sometimes lunch/breakfast on the 5). For about the same as it costs to truck things from Chicago all the way out and back, why not allow local providers the opportunity to create to-go meals ready for pickup at stops?
The other thing that nobody seems to be addressing is the incredibly uneven service that is really the differentiating factor. I've had SCAs that were amazingly attentive and SCAs that I saw twice in my two day journey. I had some DCAs that were great about coming around and taking orders and setting up meal times and DCAs that were surly and sometimes mean. I know there are union politics in play, but the sleeping car product will not survive in an era where consistent, friendly service is the norm even at the most economical ends of the market.
And, yes, of course I'm still going to be riding the Zephyr out to Reno no matter what happens...but I'm not sure if this experience will survive beyond the rail fans dying out, the folks who hate flying and the one-and-done bucket lister.