Have to agree with Mr. Norman here...might as well fill 'em up at this point....those who aren't comfortable aren't buying tickets on Amtrak (or airlines) anyway.
"Fill 'em up" should be easier now with the reduced consists ... although it is nice to see some trains growing in size. Sleepers have been marketed as "private rooms" (a form of first class travel separated from others on the train). Extra coaches ran to allow for physical distancing but now - "fill 'em up".
Back to the topic of the thread reserving seats .. Travel on Amtrak would be better with reservations. Knowing where one would sit. Knowing that if traveling with others you would be seated with them. Back to my comment from two years ago, I'd like to have a seat with a pitch - not a level seat. Tip back the base of the seat so the front is a couple of inches above the back. Seat modifications would cost money. So would a per seat reservation system. Added comfort would go a long way.
At this point the best advertisement for Amtrak vs the airlines are the problems with the airlines. Long TSA lines and airport congestion that close the gap between fast air travel and slow trains. Perhaps some of the people who have had to spend a day or two sleeping in an airport can move over to trains. The tricky part is making the experience better than going through the airport. At least with the mask mandates lifted on planes there is less to fight about.