I have been reading about these kinds of projects for some time, and even prototyped my own a while back, but one question that keeps popping up is - all these python abstractions over how html and js and dom interact tend to be extremely leaky. So, as soon as you go beyond the simple todo example, you need to manage BOTH the standard browser model and the abstraction model in your head, and all the funny ways in which they interact. Do these kinds of libraries prove useful for people beyond their authors (who have a good mental model of a framework in their head anyway because they are developing it)?
This kind of framework helps to optimize a bit for returning hypertext (iow HTML snippets) rather than leveraging a frontend system that only interfaces with the backend via an API. From that perspective, you need to be able to send HTML snippets precisely and manage more URLs that provide the snippets. React already has a pretty strong abstraction around HTML with JSX that has been generally morphed into web components. Writing the HTML components on the server using a library that maintains valid HTML is convenient, and it also means you can deploy an application without having to bundle a bunch of template files.
I will say I do think some opinions on how to structure URLs to return snippets might be valuable. Some of these frameworks leverage headers htmx sends to use just part of the page, but I think it is easier to just have individual URLs for many use cases. I've used Go and Templ in a similar fashion and one benefit with Templ is that the snippets are effectively functions, so returning the specific section and passing args is reasonably natural when breaking something out of a page.
Overall though, the goal is to avoid duplicating your data model and abstractions in the UI in favor of relying better networks, faster browsers, and HTML improvements to create interesting interfaces with simpler code.
