Oh man, I think there's so much low hanging fruit left. Browser native components for autocomplete, infinite scroll, an actual rich text editor, scroll / zoom controls, etc. would all be very welcome.
Absolutely, in terms of things that should be added to the standards and then supported by browsers, there's plenty left to do. I was mainly referring to things browsers could add on their own accord, though, like spell check, or a password manager.
(Just though of another example: Picture in Picture video playback, like Firefox recently added and Chrome and Safari have technically already had for a while.)
