In my opinion, there is a real need for a well written RoR BB system. I personally run a number of communities such as www.djforums.com. I only use vBulletin, but it really is the lesser of the evils. The code behind all BB systems that I have explored is mediocre at best. Poor coding practices, a pain to integrate into a greater site, and a pain to seriously mod (for example, replace the entire user system). vbulletin is the best solution so far, but I find it slow and bloated.
A lot of the PHP forum solutions are also old and don't implement many of the newer web paradigms. vBulletin is trying but it's just patched on and feels like an after thought. Vanilla actually seems really nice, but with a search function implemented with "SELECT ... WHERE ... LIKE", it would kill my forums with close or over 1 million posts.
So yeah, I would really like to see a good RoR message board solution.