Am I correct in thinking they are not going to advance until other 
  specifications on which they depend have been finalized? (I can't 
  remember where I heard this: maybe on this list, once upon a time.)


I don't think so, XPath 2 status says for example:

The XML Query and XSL Working Groups expect to progress this document to
Candidate Recommendation status in the very near future. 

I believe that the 15th sep drafts are so people who made a last call
comment can make a "final check" that any changes did correctly resolve
the issue, and assuming that's all OK, things will move on "in the very
near future". 

David

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