Here it comes some brain-storm, they are written by impulse, (take care with the rules-only seed ideas):
1)- sandstorms: made with cotton or similar. It block LOS like a forest. A unit can pass through. It can move with as the wind blows.
2)- dinosaur skeleton semi-buried: (a little bit of star wars tribute)
3) Paths: tracks of cracked hard soil with little vegetation. - path rule
4) Dragons teeths/tears zone: terrain with salty crystals like knives (Gobi desert has zones very salty, I saw in a TV documental how a jeep tyre blow with this crystals) or white salty zone. Could be nice visually... as a rule, maybe is not needed. Could reduce movement?
5) Dragons cemetery. A place where dragons come to die. Treated as ruined, but made of bones. Modelling: pleanty of 28mm skelly dragons parts. Khemri dragon zombies came form this places.
6) Piramids. Impasable terrain.
It is not easy getting terrain in a desert
hope it helps... and now something completly different:
some freak ideas (I am not really sure if I like them but coudl be fun for a single game),
1) In the desert you walk in circles (because you do not have a reference point bla blabla): a unit moving its full path displace its movement 1cm to the right in the desert.
2) Need water mylord!: units around an oasis (30cm, maybe) have a iniciative move to get closer to the source of water
3) Mirage: when happens a blunder, put another input in the chart to advance in a random direction