This is scary - it's like a whole new syndication format.
What is the point of renaming tagline to subtitle, copyright to rights, modified to updated, and issued to published?
Many of the changes look useful (e.g. the addition of categories), but renaming basic things (which will break existing newsreaders) is not a nice thing to do.
Anyway, doesn't mean anything to me, because I only produce RSS 2.0, and I work in Python, which gives me the luxury of using the Universal Feed Parser and getting support for all formats for free.
Also, the next wave of innovation in the syndication world is micro-content, and almost all the current ways (e.g. microformats, structured blogging) of representing it in a feed are designed to be format-agnostic - they encode their data in the <description> or <content:encoded> element, or whatever it's called in Atom. It's not super-pretty, and I'm sure the Mark Pilgrims of the world will hate it, but it works, and it means that people like me who are writing micro-content parsers don't need to care about the underlying format.