Chapter 2 of the Text Encoding Guidelines addresses this very issue.  When the TEI Guidelines were first being thought through, the concept we worked with was that the "document header" should function like a library catalogue card.  Of course it got more detailed and diverse as more types of document were considered.

In any case, TEI chapter 2 is a major, deeply-considered standard for this task.  It's the elephant in the room.  In planning a future policy for an etext repository, TEI 2 should either be adopted, adapted, or -- god forbid -- consciously rejected.  Whatever position is taken, it has to be vis-a-vis TEI 2.

As a footnote, I was chair of the first TEI document header committee from 1991, and I wrote the first draft of this part of the TEI standard.  If you don't like it, blame me  :-)   Of course, it evolved unrecognizably after my time.

Best,

Dominik