THEY
Not he. Not she. They. That is completely grammatically incorrect for a single person/other singular thing. Honestly, I'd be upset with Riot if it wasn't that dual champion that has been theorized, as IT WOULDN'T BE GRAMMATICALLY CORRECT!
So plz rito. don't maek meh sad.
I'm so sorry that your middle school English teacher failed you so horribly. Language evolves with its users; a dictionary is not a rule book, but a history text, cataloging the common usage of a word in a specific day and age. 'They' as a gender-neutral singular pronoun, including any seemingly 'plural' grammar that applies to it, is as grammatically correct as it is in the plural. Before this shift, the only similar options were 'he or she' and, arguably, 'one,' which are both clunky and somewhat unnatural. 'They/Them/Their' pronouns are a simple and completely correct way to denote one person.
Well, technically you could use "They" to talk about 
since she is a lot of souls in a body.
Or 
who always talks about him as "We"
Actually, this might be a precursor to Riot expanding the gender diversity in League's champion pool.
Even though it is technically grammatically incorrect, some transgender people that don't want to associate with male or female will use "they" to refer to a singular person in the third person.
It could be a string of champions or a herald for the watchers. (there are multiple watchers I believe) Though I'm sure it's gonna be a dual champ. :P Just in theory they could mean that. xD
But it's likely that it's going to be a character designed for the company by an outside source. I forget the name though. xD It was this really cute duo. :)
May not be that champ exactly but it could greatly resemble it.
Thank you for calling Geoffrey Chaucer a liar. “And whoso fyndeth hym out of swich blame, They wol come up"
Grammar Police are supposed to protect and serve. ~~Your ~~ You're making me sad. (also, if you were looking for a legitimate answer, it's gender neutrality)
"They" are Dha and Ma.
Well tecnically Kalista can be called it and is a single multiple person, so...
Even that, it can be a group, but doesn't mean all will be a champ. (like... they [shurima] are coming and is azir, tecnically is correct)
"They" is not grammatically incorrect, it is a gender neutral pronoun.
Say, I don't have any evidence supporting that you're either male or female. Thus when I write content pertaining to you, I should use gender neutral pronouns like "it, they, they're, their" that can also be used when there are multiple individuals relating to the text.
So the premise of your statement is incorrect; if the subject has no gender or their gender is unknown, "they" is used as a pronoun.
'They are coming" probably means that Riot is introducing a gender-less champ, likely a monster or a force of nature, or a champion with multiple individuals.
While a dual-unit champion is expected and what a lot of people want, it could also be a single person with multiple personalities :3
What you guys didn't say They when Quinn and Valor came in?
It could also be a herald of some sort. You know someone who pretty much brings an army with him/her.
Isn't it the Harrowing? "They" = spirits and such
