But rather than technical solutions it may make more sense to look at the social/culture layer first, maybe take a cue from the old-school blogosphere and popularize the idea of posting roundups or digests that end up surfacing interesting conversations.

The social layer definitely offers a quick & dirty way to give more visibility to comments, so it would be great to see that posting style emerge. Of course, it's survival would probably come down to curation support, which may or may not be available.

But even something like a digest post could be facilitated with technology improvements. For example, with the right app, I could spend a half-hour reading comments and clicking checkboxes for the ones that I wanted to incorporate into a digest post, and then when I'm ready to write about it, the app could import links and excerpts into a new post, and maybe even make beneficiary settings for comment authors.

I don't really see this as an either/or proposition between technology and social... more like "both of the above".