The notion of performing duties in a skirt is ridiculous. Ask anybody who has to do any form of manual labor (like realigning sensors, crawling in a Jeffries Tube, or performing calisthenics) in the real world and they'll tell you that a skirt is hardly the easiest thing to work in.
The whole point of Roddenberry's "spray and wear" futuristic clothing (demonstrated in TMP when the Ilia Probe comes aboard) was that 23rd century workers could very quickly get changed into more appropriate clothing for the job they had to do. In ST:TMP and ST II, the crew very quickly add field jackets when leaving the ship.
Now, the practicalities of filming ST II - ST VI and TNG were that Starfleet clothes were often seen being put away onto hangers or into drawers, but that wasn't the concept behind the creation of the skant. Clothing (at the design stage) assumed that switching clothes could be done extremely quickly, as fast as beaming down to a planet. As I said in an earlier post, the skant design was more like current-day culottes - a divided skirt, that wouldn't "ride up". Even in TOS, the mini dress wasn't actually a dress: one thigh was wrapped by fabric.
In "Encounter at Farpoint", we see Tasha in pants during the action scenes and in a skant once the adventure is over.
The idea that some planets being visited might be incredibly hot would make a casual, short version of the uniform essential. Why not something that looks like a skirt, no matter a person's gender?
Don't current navy uniforms still include a "shorts and long socks" version for hot climates?