Like Sasha Fleischman, I am agender, and they is my preferred pronoun. Non-binary identified people use all sorts of pronouns, however. It is always best to ask the person when unsure. I am glad that the use of “singular they” is being accepted by more publications.
As far as Mx, I personally don’t like it, but I will use it in preference to gendered titles when the option is available. When forced to specify a gendered title, I default to Mr, as I transitioned to male for legal and medical purposes. But I generally prefer to dispense with titles and just be addressed by first name.
What really bothers me is that there’s no gender-neutral alternative to “Sir” or “Ma’am/Miss”. I feel that these words are usually superfluous; “May I help you?” sounds just as polite and professional to me as “May I help you, Sir?” I hate to correct someone who calls me Ma’am by saying “No, that’s Sir,” because I’d really prefer not to be addressed with such formal terms at all. But I understand that many workers are trained to use them, and might get in trouble with their employers if they don’t.