...
RFC 3023 is the RFC that discusses XML MIME types. I fail to see how the
Atom syndication format differs from RSS when it comes to the fact that
people use incorrect MIME types for XML documents on the Web. I also
notice that the most recent Atom syndication format draft is lacking
information as to what MIME type to use for syndication feeds so I'm not
sure exactly why you seem to think things are different now. I'd also
point out that the RSS 1.0 spec has specified its expected MIME type in
the specification since early 2001.