I have no solution since the 2 year mark seems like a great way to tell if a plugin is still around but it’s not a blanket way to tell if a plugin is dead.

@curtismchale - http://wordpress.org/plugins/wp-db-backup/ shows 14 people saying that it works on latest WP versus 2 who say it doesn't. This statistic can be used to decide whether a plugin should be hidden or not. If at least two out of three say that it works, it should be worth listing.