First, to the original question, I have slept two and even three nights in coach several times but that was 40 or so years ago and I was much younger, more limber, etc. It was OK. Much better than a bus. It can done. But sleeper is much better, just for the experience if nothing else.
Reference to slumbercoaches. A slumbercoach was really a very cheap, very small sleeper room, it had a true bed thus there really was not that direct of a comparison to a coach seat. It was much better than coach, just not as large and nice as a standard sleeper
There were never actually too many slumbrcoaches, either under Amtrak or before. I don't mean there were not a fair lot in numbers, I just mean they were few and far between in proportion to other equipment. You could not expect every other train to have a slumbercoach, either before Amtrak or during.
There are no slumbercoaches in Canada. Back in the early 50's and perhaps before , they had "tourist sleepers" or maybe they were called something like "touralex" which were a somewhat similar idea to the slumbercoach but not l with that name. But they have been gone for years.
Gswager, it occurs to me you might have heard or read that there were still sections in Canada---if so---that is correct---but not slumbercoaches. They do still have sections on VIA. Those are the seats facing each other during the day which become upper and lower berths at night , hidden off by big thick green curtains, but no door. Like you sometimes see in old movies, like "Some Like it Hot". Slumbercoach rooms, however, have a bed, toiletries and a door.
Amtrak has never had sections, though it has, as already noted, had slumbercoaches.