Best wishes for your study. I think it is really innovative that you are asking enthusiasts for input as, while we have many axes to grind
, they are generally not biased by commercial vested interests.
Unfortunately I have never travelled on a sleeper myself and my knowledge is based on old books. e.g. Bulleid's attempt to better space plan sleeping compartments using tapered beds:- which lead to the graffitti:- "We aren't sleeping in coffins ! "
Then didn't he try to lay out beds longitudinally rather than transversely, which was another failure.
I suspect that if you had the time to research the history books, you would find that every brilliant new idea had been tried out in the past, with unpredictable results. I am not saying you can't ever improve a design, but only that achieving a quantum leap is unlikely.
I would guess that the market for sleeper accomodation is mostly luxury based, rather than utility. So piling up Japanese micro-hotel sleeping pods into a coach is probably not the way to go...........unless it became fashionable to travel that way! Now't so queer as folk !