As of now there is this nice little “resolve” button to indicate that whatever was being said in a comment has been resolved. “Resolved” however says nothing about the reason of resolvement (e.g. author fixed it or author didn’t find it relevant, two completely different things).
When a second review is requested from someone they will see their previous comments again. It would be very nice if they could quickly see what the PR author did with their comment, i.e. if something was/wasn’t done, or if the PR author agrees/disagrees with the comment. The “resolved” status doesn’t say anything about this. It’s very subjective. The PR author might also find it “resolved” if he thinks “sorry, but I’m not going to do that because x”.
My team now uses thumbs up/down emoji to indicate if something was done or if they agreed with a comment, sometimes accompanied by a comment explaning the situation. A thumbs up/down or will/won’t do button would be a great addition to GitHub.