I remember in middle school starting to sign papers with a new nickname that I was trying out. It didn't last, but I still remember that one teacher noticed and started using that name for me. It was a kind and courteous thing to do, regardless of my later decision that I didn't like that nickname after all. It seems to me that people wanting to try new pronouns should be offered the same kindness and courtesy and lack of scrutiny about how "serious" they are.