When the vertical tab sidebar is visible, it's a little odd to need to use left-and-right-oriented keyboard shortcuts to navigate between them. I propose additionally allowing ⌥⌘↑ and ⌥⌘↓ to navigate to the previous and next tab, respectively.
This could be limited to when the sidebar is visible, but it would also make sense for it to work always, just like the left and right shortcuts.
(please note that I don't think left and right should be replaced, just supplemented.)