I want to add my personal bugbear, sortable and filterable tables. And Lists of all links on a page. Oh, also expose RSS feeds again. And what about standard form controls that actually could be styled completely with css? Really, the more I think about it, the more come to mind.

While it sounds like it would make browsers more complex, I think it would actually reduce complexity, because the browser would not need even more programming capability and APIs just to enable web developers to create these kind of features themselves in a thousand variations of Javascript that adds bloat to every connection and slows down end user devices.