There will always be trade-offs in designs.
If I were planning these designs, I would have the LD coaches use the corridor coach design, simply because it would make them more interchangeable (there are a bunch of Superliners that are running California routes today, and they provide extra capacity, but do not allow the operational flexibility of allowing passengers to board/exit through those cars).
I don't foresee see them using two doors on LD coaches regularly, because in most cases, only a select number of doors would open, with a crewmember present (platforms are too short to handle the entire train). That's not to say they won't or shouldn't be built with two doors. Maybe crews will devise a plan to make the stops go faster (board through one door, alight through another).
Whether there would be one staircase or two, the current setup doesn't work because whatever the final design winds up being, you need the ability to have someone going up and down the stairs at the same time. That doesn't happen right now. The biggest backups that I have noticed are at the so-called "smoking/fresh air" stops. That's when you get everyone crowding the staircase, leaving no room for even the crew to get down to open the door.
That said, I definitely see no reason for sleepers to have more than one door per side, or a second set of stairs. That would take up way too much space and would require sacrificing sleeper rooms. Too much potential revenue loss there. I'd be curious to see a design that manages to provide a wider, straight staircase while preserving the current number of rooms and not sacrificing too much restroom capacity.
Dining cars wouldn't need large staircases at all, if they're going to be used the same way the current ones are. Lounge cars definitely would need wider staircases, assuming they would continue to have cafe sales on the lower level. Then again, I'm not sure that assumption would necessarily be an accurate one.
Also (on an unrelated note, but in response to DET63 above), don't assume that just because you don't separate arrival and departure times listed, that the stop is scheduled to be a short one.