It's an interesting idea and suggests to me crowdsourcing subjects through something like tagging.  For many years library staff have known that the manner in which subject headings are assigned for library materials is questionable, yet to come up with a better scheme is difficult.  One problem that tagging shows is that people's command of language is very different.  If there wasn't a controlled vocabulary or thesaurus, people would create numerous tags that, once combined with other articles, might be less useful than doing a full-text search.

It's interesting to me that databases like JSTOR don't use subject headings except with regard to the discipline of the journal where the article first appeared.  They depend on relevancy rankings to assist users in finding articles. Then there's the RILM database which established what it thought were fixed broad subject areas, but which are messy once interdisciplinary articles show up.

Perhaps you can show an example of a single article with the kind of system you're proposing?

Thanks.

Bob Kosovsky, Ph.D. -- Curator, Rare Books and Manuscripts,
Music Division, The New York Public Library for the Performing Arts
blog:  http://www.nypl.org/blog/author/44   Twitter: @kos2
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