I've been puzzling over this one.
I'd prefer no skirts at all. As a primary teacher I'm constantly reminded that skirts and dresses and bloody coulotte play suits aren't as practical or allow their wearer to be as active as the trouser wearer. Had a girl recently who wasn't drinking and going to the loo as getting out of the playsuit was so hard.
If you say that the trousers are the male default I'd disagree; they're more practical and to say that they're the male default is to therefore say I'm dressing male when I wear trousers. I not. I'm wearing trousers.
To be truly gender neutral you would either be anyone can wear skirts and trousers or it's all wearing one option.
As a young girl I would have at time I would have liked to have been able to have the option to wear skirts, but actually my school went a bit rad and abolished uniforms all together. Interestingly, bar a phase of miniskirts and thick black tights, the girls all wore trousers, mainly jeans and I certainly often wore boys Levi's. But that was the 90's.
I can see that the if it's the up skirting issue, the girls are being victim blamed. And it's not fair to say they and their clothes are then issue. But I don't think that's what the message is tbh. I think it's that in school trousers or shorts as a uniform is just more practical.
It's tricky personally as the daughter of a close friend campaigned successfully to be allowed to wear shorts at school (had to be dresses) and eschews dresses and skirts completely. And I really admire her.