Well, the thing is, FastHX, htmy, and holm should be powerful an unopinionated. Think of them like ReactDOM, React, and Next.js.
On the other hand, I already thought about building a component library for htmy. I'd prefer to do it with TailwindCSS and DaisyUI, or I could use for example BasecoatUI https://basecoatui.com/ as a template, because it already offers Jinja-like component snippets.
Now that I have holm as well, I may eventually do it. It's a lot of work though, finding so much spare time is hard.
FastUI is now Reflex. They essentially build a FastAPI + NextJS app combo from your code (maybe they already swapped NextJS for something else). NiceGUI is similar as well.
For my projects, I really want to avoid a big JavaScript companion app, so interactivity will remain HTMX, pure JS where needed, or AlpineJS for example. I'm also thinking about a server-component concept for HTMX with holm, but I don't have a clear plan just yet. I can think about these more now that I have holm.