I argued for this a long time ago (back when it could have easily become
part of the standard) but nothing ever happened.
My idea was to have a navigation window that would typically be rendered
seperate from the normal contents of the document (but of course, this
would be up to the browser).
The main reason for this was because I wanted my server to add the
standard (forward, back, top) type information on the fly and if there
was a <NAV> section (like <HEAD>...</HEAD><NAV>...</NAV><BODY>...</BODY>)
then I could do this much more easily. Also, it would be a *MAJOR* feature
if users had easy access to this.
In that way, each document could have it's own custom navigation interface
(or as you say, do any number of other interesting things I've never even
thought about).
--sanders