> I would also like browsers to have more capabilities "baked in;" browsers should offer keyboard navigation of ARIA landmarks (both implicit ones created by <header>, <main>, <footer>, etc. and explicit `role` attributes).

Opera 12 does that. It predates ARIA, so it navigates based on the elements available at that time. Default keys (Tools → Preferences → Advanced → Shortcuts → Keyboard setup → Edit… → Input context and shortcuts → Document Window):

• a : Highlight next URL

• q : Highlight previous URL

• s : Highlight next heading

• w : Highlight previous heading

• d : Highlight next element

• e : Highlight previous element

I can mash the keys like crazy to get where I want. The browser is super responsive, keyboard navigation is a joy to use.

The browser also offers spatial navigation (Shift + arrow keys), this navigates interactables not by their functionality, but by their apparent position to each other.