So I made another big update to Pygmy this week. Formatting of the metadata is possible now; I simply exposed the user to what I've been using to format it all along. For example, "artist - title" will be replaced per-song, and
"artist:\ntitle"will show the artist in bold text and the title in small text on a new line. Only problem is that GTK+ has a longstanding bug with wrapping labels, so a long format won't wrap to multiple lines.
Next up: optional tags, so if you have "date" in the format and it's not in the file, it won't show up (nor will the space you put before it to separate it from the title).