First, I should say that I don't really see the issue here. Staircases are built in multiple parts across multiple levels (and always will be), because the game needs to be able to give players a chance to see what they're digging into. No suggestion can change that.
Every staircase currently in the game is easy for me to envision. A few look odd or silly, but that's because they're only half-constructed. I think, though, that the way it's set up now gives players important aspects of control over how their stairs are designed that all these suggestions would remove for no real benefit.
If you are suggesting that one construction / dig order appear on multiple floors at once... that just seems like a bad idea to me. It'd be more confusing than building it in parts, in the long run. In fact, I'd say it's a
terrible idea.
Constructions take up space; they prevent you from putting other things there. The dwarves should
never put a construction on a space where I didn't specifically order it. Just because I build a staircase on one level and dig out above/below it doesn't meant that I want to waste space on another level with a staircase. Sometimes I just want to link two floors without anything else.
Most importantly, though, I will often be just below the surface and will not want to break the surface. The ability to order my dwarves to dig a purely 'down' staircase while expanding just below the surface is essential. Automatically removing the ceiling (or pointlessly requiring that I dig, then construct) sound like terrible ideas to me when the current 'dig a downward-only staircase' works fine and makes perfect sense.
Sometimes I want to easily designate the digging of a staircase that will
only go up, because (say) I'm digging a corridor that I want liquid to go through eventually. The fact that there's an open area below shouldn't have any impact on that; if I want a staircase below, I will
order a staircase below, and the game shouldn't try to be helpful by entering that order for me.
Other times I want to dig a staircase that will
only go down (say, because there's nasty liquid above me, or the outside.) If I wanted to remove the ceiling or to build a staircase on the floor above me, I'd have ordered that segment specifically.
Your suggestion, unless I'm missing something, would make both either very hard or impossible. You're assuming that players will always want their staircases to connect to anything that they can connect to, and this is not a valid assumption.
Sometimes I use stairs for traffic control. I might want to have an up-staircase leading further up, and below it, a down-staircase leading further down, without connecting the two. Why are you insisting that I must connect the two?
Personally, I'd just remove 'Up/Down' stairs. Down stairs make sense to me, they replace the 'floor' of a tile. Up stairs make sense to me, they replace the 'wall' of a tile.
You'd need a 1x2 pattern of zigzagging stairs to make a 3+ level stairwell, but so what? It'd look nicer.
That's horrible. This would pointlessly complicate construction by making it take twice as long to designate long up/down stairwells, and make it take twice as long for the dwarves to navigate any staircase longer than the (random and arbitrary) length of one layer. It would take a useful function out of the game for absolutely no reason.
If you feel that big, unnecessarily-wide staircases look cool, go ahead and use them in your own fort. Don't ask that everyone else have their fort crippled to your ascetic specifications.