It proves what we’ve always known that it is impossible to enforce women only in womens toilets. The only thing keeping men out is them self-excluding.
I'm re-reading this thread because it raises some interesting points.
This argument stands out. It took me a while to think what it reminded me of, and i finally got it. Gun laws. Whenever there is a mass shooting, there is a lot of talk about gun laws and how they restrict people's right to bear arms (so specifically in the US but also other places). And the "thinking goes" we can't ban guns because then only bad people will have guns.
And it's the same point: only owning a gun if you want to do bad things. So people literally self-exclude from gun ownership unless they are up to no good. The sign on the toilet door is a less extreme version of it, but it is the same principle. If you exclude men from women's spaces, the only men in there can't be up to any good.
But. By saying that transwomen can look however they like - and some of them really do look like burly beardy men in a wig and lipstick, how can women ever say "are you a man, you're in the wrong toilet" if we can't challenge anyone at all ever because the rule is as soon as you declare yourself a woman (or man) you are socially transitioning and that counts. Women can, then, never ever challenge anyone. To go back to the gun analogy (which may not be all that brilliant): if guns are banned and you see someone with one - they have it illegally. And can be challenged.