My thought is that HTML needs a comments primitive with date, author, subject, and references, with the resulting view (threaded, flat, collapsed, etc.) a client detail.

Or, you know, Usenet, tin.

1. Usenet was small. Somewhere between 50k and 500k users, based on my own and Gene Spafford's guestimates. More solid numbers appreciated (~1988-1992 or so).

2. It was selective. You had to be a student at a research university, or work for a tech company, or have government access, or be able to gain access to systems provided by same. Which meant you were at the tail end of a highly selective filter.

3. It crumbled under the face of multiple attacks: spam, abuse, trolls, etc. There were some defenses, but ultimately insufficient.

4. It was a pain to administrer, and for little or no gain. Which meant that few providers would, those who did charged, and they recouped minimum benefit for the effort. Ultimately it fell prey to the problem of shrinking usage and ready substitutes largely via mailing lists (relatively comparable) and Web-based forums.

5. Limited rich-format support, limited permanent content support, limited collaborative effort support. A Usenet-type functionality with _some_ support for post formatting, for images, video, and audio (but not to the point of being readily abusable), and for permanent content (FAQs, Wikis, etc.) to be usefully co-related to the primary discussion, would be useful.

I don't know that we'll ever have "one" conversation platform again. And no, Facebook doesn't count.

"Classical Usenet" was what came before, for the most part.

There also tend to be fewer comments (it's easy to see who is replying to who) so threading is typically not necessary on FB.