Figured out a possible way to have the Start screen be navigable using only the keyboard, including the arrow keys:

Overhauling the tile and All Apps list area navigation for keyboard.
In the shower I thought of this: 1. Remove/disallow focus on the SwipeView 2. When pressing left on an All Apps list item, focus the Search icon 3. When pressing left from the Search icon, switch to the tiles area 4. Focus will be set to the first tile 5. When pressing right when not in edit mod...