It is not practical. There are thousand of places to sell and buy links on the net. If the start targeting these individually, not even their entire work force would be able to penalize more than a small percentage of sites involved in link selling. The best they can do is to tinker with their algorithm, to detect unnatural links in the best possible way.
I think they are just experimenting with this tool to improve their algorithm. It is unlikely that they will start manually penalizing sites on the basis of it.