I feel that using the word "it" to refer to someone sounds demeaning, like they are an object or a weird thing. Singular "they" confuses the hell out of me because, correct me if I'm wrong, "they" is meant to be only a plural word. It confuses me whether or not someone is talking about one person or several, unless the context is specific enough. It just doesn't sound right to me grammatically. (Out of "it" and "they", I would prefer to use "they" - I actually like it because it's more inclusive/broad.) But if someone wants to be called "it" or "they" then whatever, that's up to him/her/it/etc. I've never met any other non-cisgender people in person though (that I am aware of), so I've never had to figure out what to call someone.

I think that singular they is something people should really get used to, it's been going on for ages. Using "it" to refer to people, well, that's their choice of course! With how weird my pronouns are I wouldn't mind if you called me "it" sometimes, actually.