Music notation symbols, fonts, font sources and font creation, SmuFL.
This would be welcome news, but I'm not aware of it being a "feature" yet. I don't have Fin 25 to confirm this, though. The page you point to is for a "DEV" version of the manual, so hopefully it's coming very soon!
Music Typeface Designer & Engraver - LilyPond | Sibelius | Finale | MuseScore | Dorico | SMuFL | Inkscape | FontForge
Taking what's currently there of the Maestro family and SMuFL-izing it wouldn't be all that difficult. I'm just not sure it's worth doing since an official rendition with an expanded glyph set is already in the works.