It would be nice if there was a way to get the explicit dependencies of patches
(and tags) when listing patches selected with 'darcs changes ...'. I would like
to be able to do something like 'darcs changes -p"TAG foo" -v --xml-output' to
get the explicit dependencies for all tags beginning with 'foo'.

Short of running darcs changes and then reparsing the patch files manually, is
there currently any way to get this dependency information?

I agree having explicit dependencies available via XML would be nice. I'm
marking this as 'deferred' for now since it's a wishlist item.

At first I thought this was something complicated involving actually looking for
dependencies, but now I realise it's just the dependencies supplied by --ask-deps

This doesn't sound too difficult; see Darcs.Patch.Viewing (I think)