I think one of the confusions here is that people think that these exemptions in the Equality Act are for service users (ie people).
They aren't. They're for service providers (ie businesses or local councils or the NHS or whatever).
If a service provider decides to make all provision unisex, then the only thing you have the right to do under the Equality Act is not go there.
You might have rights under another Act, of course - for instance the NHS Acts entitle you to single-sex wards under some circumstances. But you can't complain under the Equality Act that someone is not discriminating.
There are no circumstances where the Equality Act requires anyone to make a single-sex or sex-segregated provision. They are allowed to under a list of exemptions (11 of them), but there is no requirement on them to do so and they can choose not to. Yes, that means that your local council could declare that the changing rooms in the gym or the swimming baths are all unisex!
There might be an argument that a public-sector organisation could be obliged under the public sector equality duty to segregate provision in some circumstances - but that could only apply to a public-sector organisation (so a private gym operating unisex changing rooms would be completely within its rights to do so).
On top of the single-sex and sex-segregation exemptions, there's an exemption to the general rule that you can't discriminate on the basis of gender reassignment. That can be used by, for example, rape crisis centres. They are, again, not obliged to used it, but they can if they want to. Once again, the service users, (ie the general public), have no right to services that discriminate; the service provider can if they want to, but can choose not to if they don't want to.
What this case is all about is, when an organisation is using a single-sex or sex-segregated exemption and is not using the gender reassignment exemption, what happens to transsexual people who don't have a GRC?
Transsexual people who do have a GRC are of the acquired gender, ie are (legally) of the sex they say they are, so a sex-discrimination exemption can't exclude them. So, given that you have to let a transsexual woman in with a GRC, and that you aren't allowed to ask whether they have a GRC or not, and that there's no way to tell a transsexual woman with a GRC from a transsexual woman without a GRC other than by the GRC, is it gender reassignment discrimination to exclude a transsexual woman without a GRC from a women-only space when you are not using the gender reassignment exemption? And the answer was "yes".
The gender reassignment exemption is unaffected (that lets you keep out transsexual people with a GRC, so you can definitely also keep out transsexual people without one). So spaces only for non-transsexual women are completely legal - but only if you can justify the narrower gender reassignment exemption and not the broader sex exemption.
But note that this doesn't give the right to discriminate to women. It gives the right to service providers. No-one has the right to a single-sex space. No-one ever did under the Equality Act. That's not how that law works. People providing spaces are allowed to provide single-sex ones under some circumstances, but are not obliged to do so; they can elect to provide fully unisex spaces if they prefer (again, they might be required under other laws, this is just the EA).
If you want to have the right as an individual to a single-sex space, then the Equality Act is the wrong law to look at. I think you'd need legislation to create that right so you can sue a service provider for not segregating. At the moment, you can only sue them for segregating.