I originally posted this as a comment here but thought it might deserve it's own discussion.
I think that the rise of megathreads/ultrathreads/collections of threads on reddit has been a large detriment to the site.
I'm a mod for a few large subreddits that utilizes them (and I know a good portion of people reading Tildes right now are as well), and as time goes on I've started to dislike them more and more.
At first they were great - they seemed to silo off all the posts and noise that happened around an event, and made the lives of mods easier. Posts that should've been comments could now be removed, and the user could be pointed towards the megathread. Users could go back to the post and sort by new to see new posts, and know that they'd all have to do with that one topic.
I believe that this silo actually hurts the community, and especially the discussion around that original megathread, more than it helps. As modteams I think we underestimate the resilience of our communities, and their ability to put up with "noise" around an event.
The fact that we are in a subreddit dedicated to that cause should be silo enough - each post in that subreddit should be treated as an "atomic" piece of information, with the comments being branches. By relegating all conversation to a megathread we turn top level comments into that atomic piece of information, and subcomments into the branches.
But that's just a poor implementation of the original! There are some edge cases where this might make sense (take /r/politics, it wouldn't make sense to have 9 of the top 10 posts just be slightly reworded posts on the same issues), but I think this can be remedied by better duplication rules (consider all posts on a certain topic to be a repost, unless the new post has new or different information).
There is something to be said about the ability to generate a new, blank sheet of conversation with a post, that is not marred with previous information or anecdotes. New comments on a megathread post don't have that luxury, but new posts do.
Additionally, I feel like the way reddit originally conditioned us to view posts is to view them then not check them again (unless we interacted with someone in it or got a notification). This prevents potentially great (but late) content from gaining visibility, as a non-negligible portion of the population will still be browsing the subreddit, but will never click the post again.