For what it is worth, I would love this feature as well. I would like to replace a Listserv-based community discussion with the much more modern and fully featured BP groups. My hope for this plugin would be that sending an e-mail to the appropriate listening address would create a topic based on the message subject and set the topic author based on the From address (associating it with the proper BP user/group member), and replies to that message could become responses within the topic thread. Does that seem possible?
