I don't agree with the notion of eliminating the concept of gender all together. As I see it, it seems more like a statement of "you aren't allowed to be any gender", and misses the point completely that it strives for. People will always put themselves in boxes, and forcing change to prevent that won't stop it. Because of this, I disagree with those that assert no gender is valid. Social construct are not inheriently evil, and as humans we'll never rid ourselves of them, and it's foolish to try to do so. What we can and should do instead, is strive to make those fair.
That social constructs are evil is not a point that needs to be made. Gender, however, seems to have been a negative force in human history. And though people may put themselves in boxes, what kind of boxes they even put themselves in change, as in, the premise that those boxes pertain to.
This then leads to saying all genders are valid, which is really a subset of saying all identities are valid. However, it doesn't make all of them real. Most are though. Can people pretend? Sure, no harm no foul, be who you want. However, if something isn't real, then it's hard to take it seriously in the way of rights and benefits specific to that.
Since you bother making that distinction: In what sense do you mean real, and which ones qualify as real?
Personally, I don't even look at lists like that, I just go about my business and meet new people. If they say they are cis, trans, agender, or something in between or whatever, ok cool. It would all serve us better to try and look at the person BEFORE putting them in a box. Putting in a box first causes problems, and it's the big root of gender issues in the modern era.
But that's the very point of a master category. If it wasn't something you could draw instant conclusions from without knowing the person, there'd be no reason for it to exist at all. There isn't a happy, innocuous middle ground. You don't keep track of these boxes, or you make assumptions about everyone in them. Basically, it's like how it's bullshit any time someone tells you the gender and race boxes you check on forms don't make a difference. They will tell you that
legally it's not
supposed to, but actual data shows it does. The check box always matters, and if it didn't, why would it exist?
My concern is over what is perhaps some confusion about this idea of validity, or realness. I don't want any chains on the things associated with gender. All of the typically gender associated behaviors are things I think everyone should be able to do in whatever way they want, and they shouldn't even have to point to any archetypes to rationalize or justify it. When people make a discreet list of acceptable categories, that typically leads to some sort of reification, those are then considered the
real ones, typically in a sense that goes beyond social construction. Problems ensue.
I might not be as concerned about this if I were not seeing a upwelling of gender essentialism emerge among the very liberal activists and intellectuals who I would have expected to reject such things. Internal conflict is developing over LGBT issues and all that stuff resulting from a growing voice (though I do not know if it actually reflects a growing population) who take essentialist stances to be a part of accepting LGBT people and respecting their rights, vs the somewhat more established position of deconstructivism that rejects any intrinsic or natural idea of these things other than biological sex (and you could see Judith Butler and others for some interesting questions about how we even conceptualize
that).
I was just mentioning that it's hard for nonbinary people since they wish they could present as neither gender or that they could switch between which gender they present whenever they want etc, but that most people don't really understand that. I actuslly think it's "harder" to be nonbinary than (traditionally) transgender. 
