I have never seen a large open-source project that uses "forums" in a way that doesn't impose massive overhead. Without fail, forums for open source projects are dreadful while mailing lists are, with a few notable exceptions, pleasant. When I am looking for information about a project and discover that all the project officially has is a forum, my heart sinks; it ranks up there with finding out the project is still hosted on sourceforge or a mega/rapidshare/whatever clone.
It's probably about time to reinvent it again, tunneled over Websockets with a Flat Responsive html5 Retina-Aware Interhyperface or something.
What is the alternative here though? Instead of making it client agnostic, make it not client agnostic? How does that not make the situation even worse? Being client agnostic means that it doesn't matter if one particular client is discontinued. That is practically the entire point of being client agnostic...
Any solution that will be viable in the long-term needs to be decentralized and client agnostic. Otherwise you are not reinventing Usenet, you are just reinventing web forums poorly.
Edit: Aaaah, I need more sleep.
I was actually just griping.
A second problem with mailing lists is that unless you keep old messages, you generally have to go to some horrible web-based archive.
Why not use an NNTP server? Newsreaders are great at handling threads, whether they are simple linear threads like those suited for email, or massive trees with dozens of participants and many side discussions.
Those web-based mailing list archives, while usually unstyled and therefore "ugly", are well-indexed by search engines, easy to navigate, fast, and uncluttered. They are not perfect, but they offer a much better browsing/reading experience than standard web forums.
Going back to NNTP would be idea. I don't know how we actually do that en-masse though.
Instead of nested replies, it encourages "Creating new threads linking back to a post", which I find to be way more orderly than "conversation trees". They're also aiming for feature-parity with mailing lists, allowing people to participate effectively with threads by e-mail alone.
I've tried to drum up attention to it before now:
http://williamedwardscoder.tumblr.com/post/15581427232/self-...
But it's less like a technical discussion list and more like an open forum. The signal to noise ratio is pretty low.