Nobody knows what the frame of the legal challenge to the ECHR would look like, since it has not been published. There has not yet been published any claim that has been made.
And as Barristers have variously described there is no substantive claim that anyone can think of.
The only thing i can extrapolate (from my amateur legal studies) is that they could claim that the state (UK) are interfering with rights of privacy about ones sex where, it is not necessary, to do so.
That is the Goodwin case I do believe.
But the SC ruling confined itself as to where it does matter, ergo Sport, same sex spaces, and being same sex attracted, amongst other things.
I was totally confident as to where the SC ruling was going to go, as posted quite a lot.
The law is mostly logical.
I am totally confident that this is all just hot air as someone up thread said.