On the question of efficiency: it seems like a single unisex family bathroom alongside the usual man’s and women’s is an obvious easy solution. Additionally, people with disabilities can go there along with caregivers and dads can take their 4-year-old daughters. That’s a much larger demo than trannies. Replacing all bathrooms with series of single stalls doesn’t seem efficient at all.
About the resistance to unisex bathrooms. Thank you for trying to understand our point of view. I want to refer you, specifically, to paragraphs one and six above.
Other than that, I want to point out that you yourself are taking your 5-year-old to unisex bathrooms. I wouldn’t let my 10-year-old go there alone.
I strongly suggest getting the perspective of your elementary school administration as well. Our elementary school is very liberal, but if there is a boy in the girls’ room, as my kids explain, “everyone freaks out”. That’s for a good reason because he’s surely up to no good.