I've used they/them pronouns wherever I can online for years. This started in an IRC chatroom. There was a custom where everyone would copy a short intro about themselves for new people. Mine happened to not identify my gender.

One person went crazy. Demanded I tell them. Looked up my picture, still couldn't tell. Left in a rage when I refused. It made me consider: why should it matter? How would you treat me differently?

So I opted out, even though I was cis.