rel="nofollow" attribute

Google and others are introducing a 'rel' attribute value that refers to 
a document that shouldn't be indexed by search engines.  (See 
http://www.google.com/googleblog/2005/01/preventing-comment-spam.html 
for more information on why they're doing this.)

Should this, or some alternative mechanism that achieves the same ends, 
be included in XHTML 2.0?

Regards

Dave