don’t get it.
It seems like a good solution would to be to have three sets of showers in high school (and I bet one would be quite tiny). One shower would be for boys only. One shower would be for girls only. Make that determination on genetic loading and “equipment.” One shower would be for anyone who wants to use it, boy or girl (this is the one that would, predictably, be tiny). It would (metaphysically and physically) be between the two locker rooms. So if you want a single-sex shower, you can have it. If you want an “all comers” shower, you can have that, too. You can be inclusive toward everyone!
Or, just put a small stall in both boy’s and girl’s locker rooms and call that the trans-gender shower. Anyone who wants to can use it. One post is all you will ever need. Problem solved! And for relatively very little expense.
Given the HUGE costs of building schools, I suspect that this would only minimally add to costs of new buildings in terms of percentage. Hey, tax the trans community to pay for it! My guess is also that one could retro-fit most schools without huge problems–yes, it would be an expense, but actually not too bad, assuming one is really committed to transgender rights and this is not just a peeping Tom’s paradise. Again, you can just tax the trans-gender crowd and put the money in sort of a grant.