If the goal of the BBS is to stimulate conversations, not just replace the comments on BoingBoing, then it's not working. The firehose of BoingBoing posts is completely overwhelming the BBS, making it difficult to start a thread on anything else.
Perhaps the default should not be to create a thread for each post in the forum. What if the default link at the bottom of each post was something like "Respond to this post in the BBS," which, when clicked, started a new thread? That way, the readers would decide whether a particular post was worth a conversation, or not.