I don't love the idea of implementing common app state logic via attributes. It probably works a lot better than I'm assuming, but it feels hacky to me. Like it can't solve every problem you'd actually encounter when making a complex app, so eventually you'll need to fall back to using javascript, and possibly a framework or three...on top of htmx. But it does seem like this would be fun to play around with using PHP…
I found HTMX a few months after, and had it doing AJAX in probably 10 minutes. It has been unbelievably easy to use and helpful.