Ms. Moroz may have had an interesting trip, but platskart is not the lowest you can go, I'm afraid. There is still, at least there was in 2001, "obshchii vagon." A wonderful cattle car for 81 passengers. Like platskart, it also has no doors, however, there is no assigned seating, no padding, the wall along the side opposite the benches has seating, and there is no "provodnik." The lower benches are also for sitting 3 across, though on the upper bunk you have to lie down as there's no room to sit up. I know this from personal experience, my first time travelling between Samara and Saratov.
One acquaintance of mine here also swears he's seen a triple-bunk car. I can't imagine that one.