Having just returned from an Auto Train trip, I spent my first night in the upper berth of a Superliner bedroom. Never again, and I routinely use the upper berths of Viewliner roomettes. Once I was in the berth, sleeping was fine, and I wasn't claustrophobic or anything. It was just that the headroom up there is so low that I couldn't contort my body properly to climb down the ladder witout hitting my head on the ceiling. In fact, while I was twisting around trying to get my feet into the ladder, I rolled off. Fortunately, the space is so tight that I didn't fall far, and indeed ended up merely sitting up on the mattress of the lower berth, but I did get a sore wrist and a couple of bruises. My wife told me to sleep int he lower bert, and she just ended up sleeping in the chair. Fortunately, it was about 4 or 5 in the morning, and we were going to wake up at 6 anyway.
So I cast my vote firmly for the any replacement sleeper cars being single level with the headroom similar to that of a Viewliner.