I kinda see it. As a non HTMX user, it kind of feels like a “build your own” HTMX substrate

I could see it used for something like that. But it is more general as it can act upon any HTML element. So, you could use it for masking an input element or any other local state based element. Granted, it doesn't need to be limited to local, but at that point HTMX, Datastar, html-form, etc might make more sense.

html-form is the one I made out of those and it is more single focus using the native platform.