FWIW, one of the presenters at the Philadelphia Trans Health Conference specifically stated preferring to be referred to as "it." It was a very nice person and was good at organizing the two sessions I saw it at. Its presentation was decidedly gender-neutral: long hair (pony-tail?), black lipstick, light colored vest with a dark necktie. The name it went by was about as neutral as you can get: "Null".
+ + +
* Writing the above was hard -- chalk-screeching-on-blackboard hard. Every time I used the pronoun, I had to force myself, because I felt like I was denying Null's humanity.
* I wonder if it would be a little bit easier if we used the convention of always captializing "It" (or "Its") when the antecedent is a person.
+ + +
This got me to thinking about the whole "preferred pronoun" thing.
Language (well, spoken language) is a way of assigning meanings to sounds so that the person hearing something will understand what the speaker intended them to understand. The critical thing is that the speaker and the hearer have to agree on what those sounds (words, phrases, etc.) mean. Not just interms of abstract meaning, but in terms of their social effect. (Language is at its root a social phenomenon and is fundamentally about regulating social behavior.)
So when someone announces that they wish to be referred to with a particular pronoun - whether "he", "she", "they", "it", or "ze", or whatever, the question is: what does that mean, esp., what does that say about how that someone wishes for us to interact with him/her/it/zer/whatever?
We generally think we know for "he" and "she." After all, in non-trans society, if someone is called "she" (or has a female-identified name), we assume the person is female, and we have a whole repertoire of behaviors (being a computer person, I call it a "protocol") for interacting with them. If that someone is called "he", we have a different set of behaviors. So if someone whose appearance or history would incline us to use "she" to refer to them tells us they prefer "he," we (rightly or wrongly) assume they mean they want us to use the male protocols with them and not the female protocols we would have unthinkingly used if they hadn't said anything.
But if someone says they prefer "they," we don't have a set of protocols for interacting with a specific human of unspecified or neutral gender. Invented gender-neutral pronouns have the same problem, but add that people have to learn new grammar rules. This isn't to say that we can't have a generally understood way of interacting with gender neutral humans, but coming up with one and getting it widely accepted is certainly a much bigger project that just asking people to use a different pronoun.
For "it", we do kind of have protocols, but are about treating the antecedent as an object, something with no agency and which we don't listen to. (Would it occur to us to respect the agency of a doorknob.?)
So when someone (e.g., Null) asks us to refer to him-/her-/their-/zir-/itself as "it", how exactly does It want us to interact with It, and how does it differ from what It would expect if we agreed to use "him" , "her," or "them"?
(Yes, it would have been a good thing to ask them, uh, It, at the conference. Except that it was a mob scene and I was punch-drunk from 3 days of interacting with thousands of strangers. And I didn't think of it until now.)