I have a doozy of a suggestion for you.
...add the same functionality for PREFIX SETS.
Sounds pointless? For instance, using books as an example, I have two prefix sets: Fiction and Non-Fiction. Within each I have separate prefixes, eg. mystery, fantasy under Fiction, and biography, nature in Non-Fiction.
If I could add the Prefix set, users could view all Fiction or Non-Fiction threads regardless of the actual prefix.
What do you think?