I think that leather details look fine if they’re tasteful. Same thing that I think about sequins, neon colors, etc. A leather band on my Shabbos skirt or fake-leather pockets on my sweater are not the end of the world. They’re not loud or flashy or attention-grabbing.
Leather doesn’t have to be masculine. My mom wears a leather jacket that’s very tasteful and feminine- nobody would ask her why she’s wearing a guy’s jacket. I also don’t think it has to be inappropriate, either- in general, as long as it’s in good taste… and that’s definitely possible with leather.
I also think that in general, as fashion moves, things become more or less acceptable. As styles change and people start wearing new things, they enter more and more into the realm of the mainstream. And personally, I think that’s okay. Obviously it’s within a person’s rights to dislike leather or puffy skirts or neon green, but if people wear it and it’s newly common, it can shed a lot of previous associations and become perfectly fine. To be honest, I don’t see my friend’s leather-panel sweater and think, oh, she looks like she’s wearing guy clothes. Styles do change and with them so do our mindsets.