I want limited reactivity in the DOM/Web Components

Currently we have to use a library like React, Vue, or Angular to get the basic concept of reactive elements. It would be great if browser developers could enable this key feature by implementing some kind of reactivity within JavaScript and the DOM. This way, we could author very basic reactive apps in pure HTML/CSS without needing a library.

As a reference point, jQuery brought us the simplicity of querying elements via CSS selectors that browser devs later implemented in querySelector() and querySelectorAll(), which allowed us to move away from a monolithic library like jQuery and use pure JavaScript again. So, can we do the same with reactive apps? No more giant libraries and overly complicated build systems for a simple form!

I have no idea what this would look like, but we have JS modules now (yay!) and I trust the browser devs to find a solution I can't even think of yet.