The idea
Alongside the built-in styles, let you upload a Citation Style Language (CSL) file — the open format thousands of journals already publish — and have Folio format your in-text citations and bibliography in it, the same way it does the standard styles. Your niche journal's house style becomes a first-class option instead of something you fix by hand at the end.
Why it matters
There are thousands of journal styles, and the six or seven everyone knows don't cover the one your target journal actually requires. Right now that means reformatting a reference list by hand at submission time — exactly the moment you have the least patience for it. Supporting CSL means "format for this specific journal" is a dropdown, not an evening.
Where we are
On our list. Folio's citation engine already renders multiple styles from structured data, so adding user-supplied CSL is an extension of something that exists rather than a new system from scratch. The main work is a safe, validated upload and a good error message when a CSL file is malformed.
Upvote this if it's on your wishlist — it helps us prioritize.