This epic is done when backlink markers are no longer a risk to subreferencing.

When a ref is reused, the default rendering is to show backlinks with a rendering like "1.0 1.1 1.2" in the reference list. Each backlink points back to a footnote usage in the article, but the marker is notably not present in the article.

We've seen many sites override the default backlink markers, usually choosing "a b c" letters, but there are still 900 sites which might be using the default "1.0" markers. Our working theory is that we should make "a b c" this the new default, to make conceptual space for subreferencing numbers. --> T383039: Change the default for backlink markers to `a b c`

However, most languages have their own alphabets so would need to customize the backlink markers. The current customization mechanism is arcane (example) and should be gotten rid of, so we've been prototyping a community configuration page which loads alphabets from CLDR to allow admins to comfortably customize their site's markers. --> T381465: Investigation: Plan fallbacks for Cite when lacking Community Configuration or cldr