Hello Arlo,
this is a suggestion/whish list, the option to have a hierarchical way to organize the Songs in folders and subfolders. Like books of songs per author, or genre or any other classification method.
The set lists could be used for that, but there is no chance to have a hierarchical structure, like lists and sublists.
Thanks for your comments.
I think the smart lists will accomplish your goal here. You can create a smart list that sorts by Artist, and then it will be grouped with a heading for each artist. Same with a Genre custom field or any other field. Sorting by Tags is special: since a song can have multiple tags, the song can appear in multiple sections in that smart list.