Have had a quick scan of the judgment. A few preliminary thoughts:
Judges cannot ignore or re-write statutes simply because they do not like them. The Sex Discrimination Act was amended to include protection on the basis of gender identity. The judge cannot decline to apply this because he or she does not like it. Once a statute says or has the effect that 'woman' is a sex category and a gender identity category, the claim, in a case like this, for discrimination on the basis of gender identity would seem to be clear cut. The question is whether there is a further mechanism in the statute for that discrimination to be permissible. In the SDA, such mechanisms exist. However, it appears that the respondents' (ie, Sall's) main argument was not based on those mechanisms; rather, it was that any discrimination against Tickle was on the basis of sex. The difficulty is that this is seeking to introduce, via the back or even front door, the argument that woman has only one meaning. But that's not what the SDA says.
The case also turned in large part on whether the federal parliament had the authority – power – to amend the SDA. This authority comes from the Australian Constitution, which sets out the matters over which the parliament may make laws. This argument is not based on any substantive evaluation of the law, but whether the parliament has the authority to pass it. The judge held that the amendment was constitutional. I don't have expertise in this area, but I suspect the argument that the amendment is unconstitutional might be difficult to sustain.
In terms of next appeals steps - as this is a Federal Court case, heard by a single judge, the usual mechanism would be to appeal to the Full Court of the Federal Court (where three judges would hear the case). After that, the next (and final) step is an appeal is the High Court of Australia. What I don't know is whether there is an appeal route direct to the High Court, to bypass the Full Court. That said, I'm not sure whether the respondents would find success in the High Court, because none of the above analysis changes in that court. The High Court cannot disregard the statute. There is also the question of whether the respondents could change their pleadings, for instance to argue that there was no indirect discrimination because the measures fell within exclusions in the SDA.
That is, I suspect that what Sall really wants is for the SDA to be amended. Politically, the case may put pressure on the Austrailan government to provide greater clarity on the interaction between sex and gender identity provisions in the SDA. Of course, one risk is that clarity is not in the direction Sall wants.