Edited. I usually omit he or she if I don't know the gender of the person referred to. I used he in that byline (I used the author in the main phrases) as the generic pronoun (i.e., any author of such a single-div experiment), but that may not have been clear from the context.
I find "they" almost always works fine as a gender-free singular pronoun.
"it"
"that thing"
"the human"
"this being"
"They" is a widely accepted gender-neutral (or unknown) pronoun, none of those things you typed are.
Only the first one is a pronoun, and it's one generally reserved for nonhumans.
I'm sure there are people out there happy to be called 'it' (or even prefer 'it' over other pronouns) but not very many. 'They' seems much more neutral to me.