I think HTMX is a great fit for forum software. Forum websites mostly deliver non-interactive content in the form of text and maybe some audio, video, or image content. All of this can be represented as HTML and CSS. With HTMX you can do partial rendering and live updates via server-sent events. This gets you most of the way to the "client side" feel where things load dynamically based on user actions. The only prope…
I'd say that "Endless Scroll" is a good example of something that is... well maybe not interactive but still breaks the "just an HTML document" page metaphor that plays nice with such things.
Now, personally I find the UI compromises it takes to make endless scrolling happen are abhorrent (like not being able to ctrl-F or export the page content). But other people obviously like them.
Is that the kind of thing you'd be giving up as you move to a platform like HTMX?