I haven't seen this in SO (except for the review history). Furthermore, the current edited by in SO also shows the last edited person, just like Q2A.
Regarding changing the algorithm to the maximum edit is something that probably you could find useful but I (and SO) don't think it makes sense for the core (or the theme, as you mentioned again in your comment). Apart from the feature itself, implementing that logic would require to count the amount of edits that EACH user will have in EACH post. So that means even more processing.
Regarding the "other problem" which is showing the "selected by" replacing the last edit, I don't think that is a "problem". I'm perfectly fine with that: it makes sense and is efficient. If you want history, you can leverage the event module for that.
Anyway, it is quite suitable for a plugin. In fact, I'm currently working in something somehow related to that (tracking amount of approves, rejects and edits per user). So in a separate page I display the post metadata and, as another metadata line, I show the "approved/rejected/edited by" line. Unless the theme is a mess you can do that with a layer.
