Those are the Slumbercoaches that jis mentioned a little further upthread. If you want to refresh your memory, or for those unfamiliar with the concept,
The Wayback Machine has an archived copy of a 2006 NRHS Bulletin that dives into Slumbercoaches pretty deeply.
Regarding resurrecting a version of the Slumbercoaches for use today, the author writes about his experiences using them-
Amtrak started using Slumbercoaches in 1973, and, by 1974, had moved all of them onto routes that traveled no further west than Chicago and none appear to have been more than one night.
That sort of jibes with thoughts I expressed regarding the new NightJet pods/mini-suites-that they would not be very comfortable on longer routes. I can't imagine spending nearly all of a 46 hour trip on the Builder either laying or sitting in bed.
Here's a shot of what appears to be an upper berth on a Slumbercoach-
View attachment 29848
img src - train-museum.org
To start, I think the Slumbercoach concept could be carried out in a much more aesthetically pleasing manner today. Also, ditch the toilets and sinks; eliminating all that plumbing should make for an easier car to service. With the extra space, widen the corridor a bit and make the seats and beds wider as well.
Provide a communal rest room as well as a communal shower. I've seen videos for transport in Japan that featured a pay-as-you-go shower. Perhaps, if new Slumbercoach chambers utilized key cards, those cards could double as a sort of debit card, permitting each user, maybe, 10 minutes of shower time, with the option of paying for more time, if desired. Similar to a coin-op car wash. You start to lose revenue space by providing a shower, but I'd be curious whether the loss would be particularly significant.
Install a fold-down table/work space, a couple of power outlets, and decent wi-fi and I think you've got a winner.
To keep fares down, separate the transportation from the food. If a train has a café, the rider can avail themselves to that. Or, like on NightJet routes, allowing Slumbercoach riders to order à la carte meals to be prepared and delivered to their space. Or, if a rider is content chowing down on a Costco-sized bag of hot pork rinds all the way to their destination, fine. Or, and I know some will hate this idea, vending machines.