Regarding "duplicate" links: arguably they're not duplicates, of course; that's a list of recent posts, and there's one link for each post. Could we collapse those down to one per thread? Yes. Could we make that one the most recent one? Yes. Would that query be slow? I'm not sure, we'd have to try it.
Regarding sorting: we've thought a little about that feature. It's tricky, as you probably would also want to be able to limit the length of the list (you wouldn't want all posts with zero answers to the beginning of time, for example, nor would you really want the first six pages of sort-by-forum-name to be the Ant forum.)