I just got back from a round trip on a Viewliner-equipped train going to and from Florida.
Going down was no problem. The suitcase easily fit into the space above the hallway.
During our time in Florida, my parents gave both myself and my teenaged son some presents for our birthdays, which caused the same suitcase to be a lot heavier and thicker. In fact, it technically was against regulations as it exceeded the required width, and it also might have been more than 50 pounds. I could not have checked it because I needed the overnight toiletries inside and a change of clothes for the second day of travel.
The crew at the station gate in Tampa did not give me any problem, nor did the attendants who were involved in boarding us and showing us to our compartment. The joke was on me though, as it took two of us to lift the dead weight suitcase over our heads in the narrow space and then turn it 90 degrees to get it into the storage space. Somehow we did it, and then we had to do the reverse to get the suitcase out long before our destination. In our case, I was still glad not to have checked it because we had a very tight connection in Philadelphia with another train, one we definitely would have missed if we had to await checked baggage.