As a librarian, one of those who have enough hubris to attempt to organize the information of the world:

You're asking for a classification scheme of human thought. Libraries did it years and years ago -- perhaps the all-around best is SR Ranganathan's Colon Classification (named after the punctuation mark, not the anatomical part). Second best would be either CA Cutter's Expansive Classification or its offspring, Library of Congress. Dewey Decimal or its offspring, Universal Decimal Classification, isn't comprehensive enough. Besides, there is NO scheme that could deal with either the emphasis on music OR the rapid change of subjects within a thread.

Nobody is going to sit down and assign classifications to the posts. For one thing, it's not something that can be automated and there's no money to hire someone. Secondly, it MUST be done by an outsider -- you can't leave it to the author to decide, and this would slow things down to less than a crawl. Thirdly, like human thought the threads are dynamic, not static as a book is.

Even assigning "subject headings" -- Lyrics, Music Chat, etc. -- would be difficult for the same reasons. We've all seen threads moved from BS to "above the line" and back down.

What are called analytics would help, but again, who decides and who will do the work?

The Mudcat is a reflection of only a small, a very small, part of the Internet as a whole. Libraries in the US are facing a shortage of trained librarians and one of the issues is that so many of the library school grads are going to work for Yahoo or Google or similar companies -- they've found that libraries have been successfully organizing information for a very long time and THEY are paying a lot better than libraries ever could. The Internet has brought unorganized, chaotically arranged information (and non-information) to people's homes. Some people are trying to organize it and they have had a little success, but the dynamism of the Internet, its ever-growing, ever-changing faces defeat them in the long run.

It's like Heraclitus, saying that you can't step in the same river twice. And it's also, as Heinlein noted years ago, the Crisis of the Librarian.