I have long longed-for a reddit styled forum. Threaded, lightweight comments (kill "signatures", whoever thought that was a good idea), with the same sort of new-post-bumps-topic forum style.
It looks like Disqus is part of the way there, depending on their API you could maybe even hack together this functionality without having to write much of this yourself.
None of the 10 year old forum communities I can find use threading. Are you aware of any? To me, this indicates that threading isn't sustainable in the general case of online communities that type paragraphs to each other. Programmers love it as a data structure, but it's just too confusing for everyone else.
I think most people are perfectly capable of understanding threaded comments. It actually seems a little degrading to say that they are too confusing for non-programmers.
What? I can't say I've ever seen a "forum" employ threading at all because no forum software supports what I'm describing. Unless you mean that like in mailing lists (which is an example of what you're asking for) or that disgusting nonsense called threading in VBulletin which is absolutely not what I'm talking about.
I mean, reddit itself proves that it's not unsustainable in a general case. I honestly don't know how reddit's comment system is confusing to anyone. (What I'm describing is literally just reddit but replies bump the topic, and there would be less volume as they're topic/question driven forums).
Besides, are you arguing Disqus has implemented a bad idea? Because they're more or less doing what I'm talking about, but instead of having "multiple topics", it's just attached to a blog post. Imagine a listing of blog posts where the "post" is the "topic starter". Bam, it's done. You have a "forum" with topics and replies that are threaded, organized and voted on for accuracy. That's my biggest problem with forums is that anyone can post, there's often no moderation (and if there is, it's not for correctness) and people say just asinine things when they think they're correct and don't stop to think about what they're saying or whether or not they're qualified to be giving other people help.
edit: Oh, you think reddit has bad UI. Um... I mean, you did disclose it as your opinion. I love it. It's minimal, it's fast, it's content focused and it's pretty easy to use. It's certainly not flashy, no, but then most phpbb2 forums go the exact opposite route, where content takes up 1% of the physical page space, there are gaudy signatures and grandiose themes. Most people are used to hierarchical outlines. Basically anyone who has ever been to school or read a reference paper/document/manual of any kind.
It looks like Disqus is part of the way there, depending on their API you could maybe even hack together this functionality without having to write much of this yourself.