Space would really be 82 deep once I added the door. Here is a pic to give an idea of what we have now. Ignore all the wires.
I can enlarge the opening of the space over the stairs. I've thought of putting doors on the left side of that space, but then you'd need to get a ladder on the stair landing to get to anything. Hence. why we're thinking 27" dia lazy susan kind of thing. I'd still lose the corners and back 13" or so, but it'd be much easier to access whatever we did put there.