Hello to all here. A thought or two, partly echoing a few things already hinted in previous posts, and less from a technical than from an editorial perspective:
In many ways, what I hear being imagined is the crossbreeding of a periodical electronic publication with the web archive of a listserv, and/or with something of the alive listserv itself. To me, the most useful modification of the existing thread-and-riposte structure would move toward a) much greater frequency of publication, and b) compression of published units (even short single paragraphs of 150-300 words can be effective if guided intelligently).
The tricky part, from an editorial point of view, will be managing the material: the amplified evolution of the site will depend partly on active solicitation of new participants, and this can be more labor-intensive, in certain ways, than the solicitation involved in periodical publication. Joe's email database idea is a good one, I think, in so far as it will assist in generating flows of initial invitations to join and rejoin a conversation.
Another editorial function may involve ensuring that contributions, while 'spontaneous' in one sense, will not be as debilitatingly spontaneous as the base level of posts to an average (say, later-stage) listserv. All here are probably familiar with the terminal phase of a discussion list and what it entails. Personally, I relish those mysterious life and death cycles. But it seems to me that the conversions imagined for ebr, as I hear them, involve moving away from periodical 'rigidity' without abandoning the new format to 'absolute' autopoiesis.