EDIT: Also in the Ambitious column: Give the moderators the ability to move a whole comment thread between posts, preferably to another subreddit (so we can create /r/meta and dump a bunch of this old stuff there), preferably with a replacement comment that automatically links to the new location and has space for a moderator comment explaining the reason for moving. This would be better than deletion in a lot of cases.
EDIT: Also in the Ambitious column: Give the moderators the ability to move a whole comment thread between posts, preferably to another subreddit (so we can create /r/meta and dump a bunch of this old stuff there), preferably with a replacement comment that automatically links to the new location and has space for a moderator comment explaining the reason for moving. This would be better than deletion in a lot of cases.