Is it a word yet?
This is a question that occurred to me while writing the first sentence of the last paragraph of the previous post. It seems like a horrible non-word, but it's going to have to become a word. The only question is when. I hate to tell you. Unless one is willing to make oneself look bizarrely stilted, one is going to need to resign oneself to "themself" achieving wordhood.
ADDED: Some people in the comments are going on about how "you" is used to refer to one person, because we don't have a singular second person pronoun, and "them" used in the singular is a solution to the problem of lacking a gender neutral third person pronoun to refer to one person. But that shows why "themself" will become a word: "Yourself" is already a word! You don't even notice how it feels wrong to say "yourselves" when you're talking about only one person. You instinctively know to change the "-selves" to "-self." The same thing will have to happen with "themselves."