While skepticism is healthy, I don't understand how you can say with certainty it will not work.

A hypothetical technology that could very accurately determine the sex of a brain would seem to be a boon for transgendered people. Early detection could mean better treatment and less suffering with fewer cases of desisting.

I do hope for your optimistic scenario, but I do not expect it.

It would be much more likely to reveal that the idea of a "female brain in a male body" or vice versa is incorrect.