I'm pretty sure I've said this on previous mentions of htmx, but I'll say it again: this reminds me of the old SPF framework youtube published.

http://youtube.github.io/spfjs/

SPF was a bit more focused on being easy to merge into an existing server side app.

I am glad to see this and hope it has some legs. It could help free us from the need to write every UI in JavaScript(ish).