I can't think of any examples that need extended links. All the examples are expository and don't correspond to actual document types. I still don't get it.
Unidirectional links are great for everything else.
That's what Netscape is doing to some degree. I will try to create a version of XArc that is RDF centric. I would encourage the readers of this list to reread the RDF syntax spec with an eye to using it for linking. That will allow us to discuss whether RDF should play a central role in XML Linking. The thing to keep in mind is that the RDF model can have many different serializations.