The Atom syndication format is now stable, December 2005, the Atom Syndication Format was issued as RFC 4287, for more info see http://en.wikipedia.org/wiki/Atom_(standard)
While support for generating Atom feeds would be nice more important is the ability to import Atom feeds, XML::RSS doesn't have Atom support so this would probably mean adding an initial feed type detection stage before using one of the many Atom modules on CPAN, http://search.cpan.org/search?query=atom&mode=module for parsing the feed.