According to the Bugzilla search results for “xlink”, WebKit already seems to support XLink — but only in SVG documents. I propose that it should be allowed in any XML document; then, no munging to XHTML (e.g. with XSLT) would be required for an XML document with CSS stylesheet to be rendered as-is in WebKit.
Currently it is not possible to get any hyperlinks in pure XML documents without mixing with XHTML because there are no CSS extensions like Opera's -o-link and no xlink support. This is a serious limitation.
Would it be possible for you to provide a simple test case for this?
Bugzilla has experienced amnesia today, here is a comment that was lost:
--- Comment #3 from Thom <firstname.lastname@example.org> 2009-08-20 12:34:53 PDT ---
is an xml document that's used to showcase mozilla's xLink support, which is
better, but also poor.