I almost want to apologize for this suggestion beforehand for how much processor it would inevitably kill (or if such an idea was mentioned in a previous thread, I looked I promise!)
So here we go: We know some people look at desert fortresses as a huge anomaly, being able to dig into the sand without it collapsing. So here is what i had in mind: Sand acts like water. Slower albeit, but still like water.
when you dig into sand there should be a period of time where the sand wants to fill the void by slowly pouring in. This action could take several dwarf days to fill in 1 tile promoting the dwarves to build walls around the current level and making sure that any levels above are made out of a more solid material.
If you were to say, dig a staircase down through 6 levels of sand all the layers would want to fill in the lower levels and they would fill this area much more quickly and deadlier than say a 2 level deep staircase. the poor dwarf would sit there suffocating unless someone comes and digs him out. This of course could put the rescuer at risk.
This can also be applied to snowy areas to add a little more flavor to it. Trying to wade through areas of "thick" snow, about 3-5 fullness on the fluid scale, would greatly slow down a dwarf, if say an avalanche or blizzard type event would happen that would quickly bury the dwarf, he could run the risk of suffocation being burried under the crushing weight of the snow. Snow obviously would have a much more static movement than that of sand Perhaps being limited more by a regions wind speeds as opposed to current fluid dynamics.
Fullness of this Solid-Fluids could also give rise to such areas as dunes, or snow banks. a full area (7/7) would be treated as a full wall tile, which one could walk across. Tiles that are half full or mostly full (3or4/7-6/7) could be traversed much like ramps would, while finally near empty tiles would always be waded through slowing down the dwarf.
These areas of course could be mined (shoveled) as not to hinder movement. They could also use wind dynamics to determine how the sand dunes and snow drifts form. When you reach a map there could be set heights of these features and wind would push these into higher areas, and they would tumble down to the lower areas. Yeah I know I can't really think of a good way of describing this action, but keep in mind also that this should happen at a MUCH slower rate than water, true changes taking place over the course of SEASONS as opposed to seconds... unless of course weather hits...
This could raise small disastorous events akin to a siege, but against mother nature herself... Imagine getting a warning similar to a siege... A sandstorm is comming!... Beware the Blizzard!... In which the shifting of these surfaces can happen fast and deadly, What was a safe tile a moment ago is now a suffacating tomb. The player might not even be able to see under the blowing detritus until the storm settles. If you see one of these warnings you would have about a week to make sure everyone is inside and the doors/hatches are locked lest any flying sand and snow begins to pour into the fort.
Whew it was a long one! I just think that something like this could definitely spice things up for the harsher regions. Nothing necessary, but most definitely "fun."
additional note: the "gather sand" job would NOT remove any sand from the pile. Also the sand effects would be for regions recognized by the game as Desert or Badlands and the like, and would NOT effect say river sand or sand patches in Forests and fields.