I've updated the details here to reflect our thinking on implementation. We're aiming to keep things in line and consistent with tools like Adobe Acrobat, so we will likely opt for supporting tab / shift+tab to navigate comments.

Adobe's hotkeys for comment nav, per their docs:

"Move focus to the next comment or form field" => Tab

"Move focus to previous comment or form field" => Shift+Tab

This means we'll also aim to better support how/when inputs get focused when navigating between comments.

Or at least restore our shortcut--option/tab!