Well, hmmm. I think I'd like it to have some of these characteristics:

we don't maintain multiple copies of documentation (of course)

the image is the master source of documentation

documentation in the image is kept in human-readable format - the
existing comment strings can function as the initial core of the
documentation

ultra-lightweight markup is made available to support richer
formatting & linking - I would favor something like zope's structured
text (like wikiwikiweb markup but more intuitive)

when needed, a complete set of docs in XML format can be generated by
parsing the above; any other formats can be generated from this

the standard browser is extended, or a new doc browser is added, or we
use scamper to provide a richer documentation-browsing experience
within the image

in general I am having tantalizing visions of convergence between the
idea of a wiki made up of pages which are content and/or code (my
current project), and the smalltalk image made up of classes/methods
which are code with some content. I feel it would be useful for the
image to offer some aspects of a wiki as an alternate interface for
browsing & editing the documentation (code too)

this enriched documentation within the image can be presented on the
web in the same way as the existing slick javascript browser
implementation, or by using a com.. whatsitsname.. a swiki server.
This interface also allows editing.

there is one master image always online at squeak.org, serving the
above interface over the web. This is the master documentation copy,
at least for the core code. There is a means to sync up documentation
in other images with this one (modules ?)

this master image - at least the documentation in it - functions like
a large wiki where all can update. It is the master copy on which all
releases are based.

Look at that, I seem to have some opinions on this. Thanks for asking! :)

-Simon