I don't see how Giggle can win, because making sex subject to self-ID means that Australia has no sex-discrimination law. And I understand from PPs that the only exception, on physiological grounds, to the ban on anti-trans discrimination, is in relation to sport.
Surely the most that can be expected is an obiter declaration that the law, if applied consistently, is a bad law because it has (other) bad consequences, eg failing to protect the more vulnerable sex on grounds of safety and modesty.
It's unfortunate that the case relates to an association rather than, say, a DV refuge. Because I can see the court closing its eyes to the wider picture, and just ruling on the basis that there's no harm in having a club for both sexes, provided they're all of lady gender. The harm is hard to define, because it goes back to the right of men/women/lesbians/gay men to form associations, which the law has specifically taken away, in order to force them to accept any opposite-sex person who wants in. Its literally what that law is for!