The now 13th iteration of the spec got rid of RFC 6415, requiring only a single HTTP request to fetch the information:
The default serialization format now is JRD, the JSON version of XRD.
CORS is now mandatory, so that web-applications can fetch the files, too.
Net_Webfinger now supports the new Webfinger draft, but is still able to fall back to the old system - many providers, Google among them, didn't make the switch yet.
XML_XRD fully supports reading and writing JRD files now.