Here we go...
As one of those people who have gone through a transition, I'd like to add further mud to the water.
There is a difference between Sex and Gender. The correct term for a transsexual is just that, "Trans" has transitioned "sex" the sex. If you extrapolate my current position, my birth certificate recorded my physical sex as male. The fact that my gender wasn't recorded, and indeed couldn't be checked by taking a look between my ears, is almost fair enough.
Society is in flux. In some cases it now values and responds to a person according to their apparent gender, but still segregates on the basis of physical sex. I'm probably going to get flamed to hell right now, but I can't see that segregation ever going away as long as the human race is, physically, what the human race is.
Enter on the scene, the gender fucker troup and those of the ilk that take things further, we should relate to a person as a person and not burden people with such a catagorisation. On the face of it, I can see where they are coming from; much of our social interaction is based on such segregation; ie. how we congratulate each other, whether with an air kiss or a hearty slap on the back.
If such social guidence is removed, then many peoples social interactino rule sheet gets a flame to its bottom corner ... and you can have fun watching peoples faces light up in horror as they suddenly lose their grip as to how they are supposed to interact with other people.
So, in my humble opinion, if you're going to do the job properly, you remove the M/F entirely; you don't add a new catagory, or you'll be adding catagories for every group of people that identify themselves outside the standard classifications.
Sex is straightforward. Meat and two veg, or a camel toe? Yes, there are exceptions, good old Mother nature does enjoy making life interesting. Gender ... now there you're really entering a world of catagorisational pain.