Dear Dag.
Did anyone look at the Forum capabilities of Drupal ? Or at some of the Drupal modules that add Forum capabilities.
If you add drupal to the list on the wiki, I am sure someone will look at it ( maybe me, I am considering using it for my own website as well ).
There have been some interesting comments from Drupal users on my blog-post that compared the requirements with modules and features.
In general most of these comments are very interesting and Drupal is of course a great CMS., but I think the forums (even the Advanced Forums) does not scale that well.
There is a phpBB bridge available which might be an option.
Concerning Pun/FluxBB I have also talked to the (ex)developer of Puntal who said that his software is final and will no longer be developed. Puntal relies on the authentication framework of Pun/FluxBB which also needs to be extended to use LDAP auth.
But I guess Puntal is no real option as it's no longer maintained.
Best Regards Marcus