Well, there are completely different alternatives. We can also make currently segregated spaces into entirely private spaces, for instance. But I'm not actually all that worked up about either sex seeing the other naked, either, regardless of trans status... but such things should not be forced.
Perhaps we could just add a co-ed shower or whatever for those who are okay with it. No boners allowed, of course. A guy popping a bone in the all-male shower wouldn't tend to be any more welcome.
The solutions are not always one thing or the other. Often, there are other changes available.
Trans would obviously be in the co-ed section.
And if you think all guys want to see ALL girls naked... or that NO girls want to see ANY guys naked, you're sadly mistaken. Both are pretty highly biased to what they find attractive. Even more so when they're young.
I dunno... it might seem like an invitation to sexuality for some people. But less so than you might expect. When it's every day, you tend to get less curious. And if an authority figure specifically mentions the inappropriateness of erections or any overt sexuality, I think you'll find fewer horny guys who can't handle it wanting to try it.
I mean... it's not like guys don't have external signals about whether they're horny or not. Even if you can avoid a full erection, you still tend to get partial enlargement and prejism if you're fixated on the wrong things.