I just thought of a feature. Instead of posting a link to a previous discussion, you should be able to "merge" a new thread with an old one. Perhaps the new url and post could be added to the previous post, but the discussion itself would be more "persistent". Sometimes there is more to say, sometimes the original discussion is worth revisiting, etc.
totally agree, I just reposted this here because I thought this article at LWN gave a lot more details than the previous ones.