Instead of every website needing to build a table of contents, web browsers should be exposing that via the accessibility tree.
Instead of every website needing to have a UI for paging, web browsers should be able to get the OrderedCollection and render the UI or however many pages you want.
Instead of websites having a million JS-riddled form rendering libaries, web browsers should be able to expose form fields however the user likes.
This should work for 2D, TUI, and 3D depending on browser