LW has a unique format. It is a forum-blog.
It is not a forum in the traditional sense. In traditional forums you cannot have long, essay-like posts (technically you can, but somehow the culture discourages it). Also, visually the top-level post appears separate and isn't similar to the comments. Like forums, you do have threaded comments and a karma system. Further, anyone who wants can register, post and comment.
It is not a blog in the traditional sense. In most blogs only a select few can post. On LW anyone can create a blogpost, as long as it is somewhat relevant. There is also a notion of Main, where the moderators select the best posts. And the bloggers can aspire to achieve the Main standard.
I feel that this kind of forum-blogs can be very useful in many domains: math, physics, meditation, music, health and nutrition and so on. Of course, we'd need to assemble a high-quality audience who are not afraid downvote and also have good moderators. The problem of assembling a high-quality audience can also be done in LW fashion. Write a good blog for sometime and then convert the format of the blog to forum-blog. The advantage is that the new people who write posts have a guaranteed high-quality audience and are hence incentivized to post and make good posts.
So here's my appeal to people who already have blogs with a good readership: please consider converting your blog into a forum-blog in the style of LW. It will be a huge service to the community. If you do so, please don't be shy to moderate and select the best and treat them separately.
Or is there some other subtlety that I'm missing which is preventing the creation of forum-blogs? Or are there already forum-blogs out there and I'm just not aware of them?
EDIT: In reply Randaly's comment, I appeal to LW's masters: please consider releasing an open-source toolkit that allows the creation of blogs based on the LW format.