So far as I know, Dublin Core itself is not obsolete. The Drupal project is still using them. Like with all metadata, I have no idea if any machine anywhere actually makes any real use of any of it. If someone does, it would likely be the search engines Google and Yahoo! (both of whom prefer Google's Schema.org stuff I guess).
There's been a vote to remove metadata from HTML5, but that was merely to take it out of the HTML spec, not obsolete it.
This woman seems to be one of those metadata people, and here is a very recent (2013) mention of still using DC. http://lealaabbott.com/wp/archives/750