Maybe the death of the blog is premature, but its usefulness is limited. There are good reasons to reintroduce features of the older forum idea back into web speech. This would involve beinging back threads and subthreads, context reply to comments with quoting, and a decent editor to do these tasks.
Twitter and Facebook as Social Media are nothing like this, and that is their downfall. The same problem appears to a lesser extant on You Tube. The closest design I've seen to the idea in a web site is slashdot.org. That site does not implement all that is needed, which is much more like USENET newsreaders.
There are several advantages to forums over blogs. First people don't have to read every post and run the risk of either having to deal with out of context replies or trolls, On the USENET 30 years ago people jsut modified the title to create a subthread and there were clues in that about which threads were worth reading and which were not. Subthreads with lots of replies were low hanging fruit and could often be ignored, and with some content filtering one can get ot interesting posts and ignore all the mundane, predictable posts. One metric that is quite useful is to junk or make as read or ignore posts that are only a couple of lines long and look for those posts where someone took the time to write something of length. This heads in the opposite direction of social media, but it may be the right time to head in a direction that promotes badily needed discussion.
There are blogs that support long posts, such as on many newspaper sites, but they are not managable because they are not forums, with collpased threads and suthreads, this is also true of slashdot, but with a better design like a forum but not quite. it is posible to find interesting posts from all the others on slashdot.
I think that the people who run Twitter and Facebook do not care about public discourse or its role in keeping democratic institutions. People are increasingly weary and afarid of political ideas and the cynic in me thinks that the Captialists that run these companies, and Google, and others do not really care that average people learn to reason and discuss issues, but would rather feed them political slogons and make consumers out of them. This puts democratic traditions in peril, because of the limitations of the chosen technology make its worse. People confuse their frustration with the technology with their frustrations with people. I think that the companies that run social media know this as a way to control the political thinking of their users.