At my place of work, we've sort of implemented that feature by using fixup or squash commits. That is, if a comment is made on a diff line in a PR, use git blame to determine which commit was responsible for that line of code, update the line and commit it with a commit title like: fixup! <original commit title>. If we want to update the commit message, we use "squash! <original commit title>" and put the updated commit message in the commit message body (using the --allow-empty switch when committing so that we don't have to change any code to make a commit).

Then, we can run git rebase -i --autosquash --keep-empty to handle applying the changes requested to the correct commits at the end of the review process.