This all ties in with something discussed in another thread. There I said:
http://www.bay12games.com/forum/index.php?topic=34969.msg539462#msg539462Basically, if the world is seen as divided into finite cubes of stone or free space, in layers separated by a "thin" floor/ceiling that may also be independently stone or free space, then what is being suggested here is to make all stairs fill the "cube" portion from top to bottom (instead of as currently - arguably - being composed of a "top half" and a "bottom half"), plus removing the ceiling "plate" on top of the stair. I like this, it seems to be a more consistent representation.
I see a small side-effect that may need to be addressed though. If the ceiling above a newly-constructed staircase was automatically removed, that would require the involvement of both masons and miners in the construction (it's like digging a channel on the upper level). Preferrably, both steps could be done without two separate designations.
Also, if the ceiling is removed as part of the construction, that complicates current notions of support; the staircases would be standing on top of each other only, not on the floor of each level (and so might collapse where they currently don't) - also, no floor would mean things could not be lying "next to" the staircase on the same tile.
Perhaps it is better to see it not as *removing* the thin floor plate above the stair, but merely making a staircase hole (an altered type of floor tile), which would leave the floor to function as it does currently.
In fact, the above means that the current and the proposed systems wouldn't be too different; To carve a staircase down would involve two parts: dig the role in the floor, and carve the staircase (on the level below). Constructing a staircase upwards through a ceiling would entail constructing the steps and digging the hole (and digging out the cube above, if applicable). Presumably, the steps would need to be in place to make the hole from below.
The difference would be a more consistent representation and the ability of making stairs in a single step, as has been pointed out.