What's something not possible in HTML/Web-Dev that you'd like to see?

CSS frameworks that are smart enough to only apply CSS that your site actually uses. And no, I have zero interest in compiling my own version of Bootstrap to achieve this.

A static generator in PHP that just works with shared hosting without the need for any 3rd party libraries or frameworks. Just upload, unzip and you are set.

Basic persistent key-value data storage in the browser using only HTML.

Fast, constraint-based layout as a simple rules language with optional layout handlers and calculations provided by code.

Drag and drop application building like .net Winforms.

The productivity boost of quickly making forms and only coding the button actions is unmatched. No "RAD" web framework on the web is anything near that.

A rough client cpu/gpu performance indicator may be useful.

Intersecting markup.