I agree that the Armadillo
set-up looks tight on top. I think a triple could be done, though, but only if you started at the floor.
Two feet is adequate for sleeping- I sleep in the stock lower bunk, which has less than that. Main issue is your shoulders have to clear when turning over, which they do easily.
The front bench is structural to some extent, so removing it weakens the trailer a little. You could overcome that with some solid shell and frame attachments, especially near the door.
Bottom line: possible, but a layout 7 with an upper bunk or slide-out extension seems more practical.