Implementation is pretty simple:

• User attaches an audio file to a blog post, and includes a {podcast:myfile.mp3} macro in the post. (Or possibly {rss-enclosure:myfile.mp3}
  * RSS feed entries generated from that post incorporate the mp3 as an RSS enclosure (or whatever the Atom equivalent of that is)
  * Possibly, the {podcast}

  macro allows you to add the various iTunes-specific metadata elements to the RSS feed?

Vanity feature, but it's a nice little checkbox to tick, and it can be done in an afternoon.