Description from the project's git:
Bluesky added a pronouns field to the profile record — a single freeform string capped at 20 graphemes. Fine for "she/her", useless for multiple sets, neopronouns, or anything more complex.
A popular pronoun labeler got deleted and everyone's pronouns vanished with it. Labelers are someone else's server. When they go, your data goes.
This is a sidecar record on the user's PDS. Multiple ordered sets, open-ended forms per set, author-controlled display. What you type is what gets stored. Clients that don't understand the lexicon just ignore it.