I'll admit to not reading the full thread, so apologies if this was covered already (I got just over half way through the first thread, and the last couple of pages of this one).
The Topshop policy changed at least a month ago, the email linked previously is from October, the Travis tweet didn't change the policy. Also, it isn't a loss of the female space while maintaining the men's space, it's a move away from segregated changing rooms. Anyone can use any changing room, regardless of which part of the store it is in.
In practice, people will go to the one closest to the clothes they wish to try on, unless there is a huge queue, so for the most part the one in Topshop will still be mostly women trying on women's clothes, and the one in Topman will be mostly men trying on men's clothes.
Is there a risk of someone doing something shady? Of course, there always has been. Even staffed changing rooms will not be staffed some of the time, if someone is determined to do something illegal they will do that. Almost all the changing rooms I have been in have alarms/call bells in to alert staff if there is a problem like someone perving or being inappropriate and that is still a crime regardless of the person's gender identity or biological sex.
If you have a problem with gender neutral/unisex changing rooms, that's fine, but this isn't the fault of this one person, they were just failed by a store not following proper policy.