How many times did you reply to reviewers's inline comment with simple "Done" or "OK"? There is just too much of clicking and typing for such a short message. Let's add "Done" link next to "Reply" to each inline comment in Differential. Clicking this link would create a replying comment containing nothing but "Done" text. It's the same as if you have clicked "Reply", entered "Done" and clicked "Ready". This lets both you and your reviewer know that the comment was read and addressed.