I'll rephrase that question, where do web discussions want to live?
Disconnected islands of social information exist throughout the web and beyond to other internet communication channels. IRC and Instant Messaging have been standard exchange mediums that cater to real time interaction. Email provides an asynchronous digital channel for connectivity. Forums, blogs and social platforms cater to near real time exchange for larger groups, funneling visitor attention. Social audio and video are growing alternatives to text based communication.
I've had my share of experience with forums in the past decade as an avid online gamer, enough to know that discussions break down when constrained by one never ending chain. The conversation quickly diverges from the original topic and sprouts out to more casual exchanges and goofy jokes. Even if the updates remain focused on the post topic, the information is formatted in a less than ideal, continuous stream of divergent thoughts. New visitors can't get a quick high quality answer, or reasonably understand what's going on. We knew there had to be a better way, and if there's one thing that's done brilliantly on the web, it's iterating and experimenting with different information forms.
I came across a related question on Quora concerning Twitter conversations. Should discussions on Twitter evolve to those on FriendFeed, Facebook, or Google Buzz? The following was my off the cuff answer:
Twitter is a great jump point, a focal point of concentrated attention for news and what's happening now in the areas you are most interested. But conversations about topics are too limited and would result in additional noise on the channel (unless hid by default).
The current follow model flows all updates from people you subscribe to which is subject to noise. Not many twitter accounts are topic specific. Updates cover a range of interest areas and you have to filter out what's not immediately interesting or necessary from what is.
That's where utilities like Quora, Stack Overflow, blog posts and Disqus can come in handy. The conversations can grow outside of the update service and maintain a relationship to the source. Now what would be useful is a connected or linked network from tweets, buzz updates, and posts to all the conversations that happen about them. Conversations have a way of growing in many different web kingdoms, Hacker News and Reddit are obvious sources. But add to that thousands of blog posts about a specific event or decision and all the comments about those posts. There are literally unbounded conversation locations that result from compelling posts.
But that's ok. That's what the web is designed to handle. Unbounded information growth and exchange
I'll zero in on this quoted idea:
conversations can grow outside of the update service and maintain a relationship to the source
What I refer to above is value in adding machine readable structure to human conversations. It's the motivation behind semantic formats like rdf. Relations between data can be written into the data so that more meaning and higher utility information can be delivered to those in need. A link between two resources can have qualities beyond an href, such as sentiment, topics of association, or descriptive verbs.
I see future web conversations moving far beyond text in a single language, on a single host/domain. With the growing strength of machine intelligence translators and speech to text tools, detailed conversations between people all over the world will be possible, in languages they are most familiar with. Both real time, and asynchronous text, audio, and social video will serve as viable conversation conduits between motivated minds.