The diff viewer has keyboard shortcuts for navigating throughout the diff, but nothing for adding comments. It'd be nice to add these.
The problem is that we can't select individual lines, so you'd only end up creating a comment box for the first line in a chunk.
Suggestion: A key to toggle between "block navigation" and "line navigation" mode. In block navigation, hitting the "new comment" hotkey would create a comment for the block, and in line mode, you could use shift- <direction keys> to expand a selection to multiple lines and comment on them. (I realize this is probably a bunch of work, but eventually it might itch enough for someone to scratch.)
i'll work on this