If anyone who has used (or currently uses) Calibre, these variables are set up as clickable tags: custom tag, author name, publisher, series (publication in Zotero). Once the user clicks on any of these, only the items from that specific tag would appear.

So if a user were to click a specific author, all items written (or partly or co-written) by that author would appear, which is a far more efficient way than typing each time or setting up a custom advanced search (which aren't able to be added into subfolders and beyond like normal folders).

Perhaps if custom searches could be dropped into subfolders, that would help, but if anyone understands what I'm describing above with the clickable tags in Calibre, they'd know it's hard to beat that function (but then again nothing beats Zotero for organizing my 1000+ journal article hoard).

I think I know what you mean. In Mendeley, you can filter by authors as well as tags, and being able to switch from tags to authors in Zotero to show all items published by the selected person(s) would be really nice, I think.