I do not want to distract from the possible solve Chris's Drupal offer may provide.
Though I've been distracted myself with the prospect of doing an svg based forum design.

I've seen so many excellent things in Inkscape.
I have been provoked into working on a web-store for Inkscape files.
(A separate thread).
..Back to the forum.

So:
-------------------------------------
Such a design would use as much Inkscape as possible/applicable.
  Certainly a delightful prospect!
Should present reasonable forum expectations.
Should be as backend-agnostic as possible.
  Which could mean the use of xml + xsl => svg 'portions'.
Be using a browser target priority of 1) Firefox 3.5...  ... see Browser notes below.
  Use animation where applicable, fakeSMIL <script> if necessarry.

There are significant javascript hooks in Inkscape so that xml+xsl transformations can be small routines in javascript.

Browser notes:
------------------
Firefox + fakeSMIL = ok.
Opera = ok.
Safari = ok.
IE + firefox plugin = ok. (http://www.savarese.com/software/svgplugin/).
  (Really, if an ie user is not ok with this, then can download Firefox portable).
  Pragmatically speaking, interest in Inkscape implies readiness to be .this. flexible.
There will be some script isues.
Some can be avoided by using x-browser 'modules'. eg For xhttprequest, xsl transformations.

Auth notes:
--------------
OpenID as an Auth agent. Others to follow.

Other technical mechanics:
---------------------------------
Small data references & text can be 'POST'ed to an OpenID'd session.
XML + XSL  can be xhttpRequest 'GET'ed.
This can be the basis of a xml+xsl delivery mechanism.
========================================================

?

MarkT
--
チェックアウトが、Jingle だ!
It's a Jingle Out There!