Oops, I missed this thread.
To quote myself:Discourse is an annoying try to do everything differently even if there was no actual need for that before. The UI requires Javascript which sucks for security reasons; but, even worse, the whole thing grew so fat that the only supported installation method is a pre-configured Docker container (!) which limits Discourse to Linux although it does not require any other Linux-only package.
Their so-called community does not seem to care about people doing things in a different way.
Pointless technical restrictions of usability just because it's
more modern is not something anyone should want to achieve; although I must admit that I really like the
Misago board because it's outstanding in some ways.
The Usenet and mailing lists (mentioned above) are different things than web forums, they also target a different audience. I use newsgroups on my Android device, so I'm probably out of the picture. -- That said, today's board systems make it easier to stay
trendy. I fell in love with the
Invision Power Board a while ago because its user interface is one of the greatest I've ever seen - even on my smartphone.

(A pity that DonationCoder doesn't have a responsive UI yet; but maybe mouser will use the new opportunity...)
Board systems like Discourse and Vanilla have a different target audience
again. The first time I've read about Discourse was when I set up my first
Pelican blog, it seems to be a nice Disqus replacement. Such boards may work nicely for commenting stuff or as software support forums, but the lack of structure (like immediately visible subforums/categories) makes it really hard to think of them as viable replacements for
real forums™.
The world's
biggest (regular) board (ConceptArt.org) uses the "classic" vBulletin software, its inofficial "successor" (after vBulletin 5 was FUBAR) XenForo already gained much traction and market share. Don't even dare to assume forums are dying. They're consolidating.