I think that all implementations that map ".xml" to text/xml without the charset param have to be fixed.
that Atom documents MUST NOT be served with the '.xml' extension?
It is not a bad idea, if you would like be conformant immediately.
Application/atom+xml and application/xml look reasonable to me. If atom becomes successful, it should not be difficult to map ".atom" to one of these media types.
I do not think that this issue can be solved by changing specifications. If we change MIME, HTTP, and RFC 3023, some implementation might work correctly. But other implementations, notably MIME implemenations, will work incorrectly.
-- Asbjørn Ulsberg -=|=- asbjornu@xxxxxxxxxxx «He's a loathsome offensive brute, yet I can't look away»