Basically, when there were many changes on a page you watch since you last visited it, you can show the diff of all these changes (using history or watchlist).
However, the diff often shows additions and removals mixed and much context is hidden (cf. T231698) because that's how diffs work. There are also novel VisualEditor-VisualDiffs, but they aren't optimal either.
So I propose that when you open a diff of a discussion (a page that would make use of the tools), the new comments (identified by the signature and timestamp where the comment timestamp is strictly greater than the timestamp of the base revision) are somehow highlighted on the page. (Motivation: These are the comments I am more likely to respond to.)