The plan for forums:

Step 1: Dynamic signatures - DONE!
Step 2: Signatures displayed on forum posts - in progress.
Step 3: Private forums: move the parts of forum_acces dealing with CRUD of forums themselves into core. Needs to deal with comments as well.
Step 4: Allow comment-type.tpl.php (simple 2-line patch, should go in after the theme stuff merlin's doing now)
Step 5: Ship with default sane theming for forums.

"nice to haves":
- Moderators: add acl.module into core??
- outline.module: http://drupal.org/node/128731 -- would allow placing any type of node into a forum, consistent way of dealing with hierarchies, potentially extending forum_access so it culd work for books, sections of site, etc.
- comment_mover.module -- not sure if this is core-worthy yet or not.