"it would seem that if you removed the nofollows, it would open up the site to all kinds of abuse"
That's why the author of the article suggested that they remove "nofollow" for users who have an established reputation, like SlashDot does. That algorithm would seem to be very easy to implement.
You need a good amount of karma to edit someone else's posts, so that's a non-issue. If it was an issue, the rel=nofollow should be based on the rep of the user creating the link, whether that was the poster or the editor.
You need 2000 rep to do this, which is not so easy to gain, but certainly achievable for a highly determined person. However, what @wookietrader wrote applies -- each edit is marked with the person who has done it which solves the problem.
Since you can check what user added what link (using diff), you can still use the reputation threshold. If that does not scale, just use the minimum reputation of the editors' reputations.
That's why the author of the article suggested that they remove "nofollow" for users who have an established reputation, like SlashDot does. That algorithm would seem to be very easy to implement.