Savas is blogging about an idea we've been batting around for a little while around exposing hypermedia state outside of regular resource representations. In essence the idea is that by using the Accept header clients can ask a resource about other resources it knows about, effectively supporting the whole hypermedia as the engine of application state constraint in a generic way which isn't coupled to specific formats (e.g. Atom, XHTML). I quite like the idea, but it'd be nice to know what other folks in the community think too.
As a Semantic Web enthusiast I believe you could have application/state+rdf and application/state+n3 too, maybe using ontologies such as http://vocab.org/lifecycle/schema or http://rdfs.org/sioc/services
I think it would be nice to have a standard or best practice such that a more generic client could find out which links to "follow" with less overhead.