Great idea. The big hurdle to overcome, I think, would be that people might double-sell the land. They sell it to concerned environmentalists, but those people are scattered around the world, and with nobody to verify that the forest land is being treated properly.... You could have people who buy a bunch of forests, only to learn later that those forests have been destroyed.

I guess what I am trying to say is the ECO idea would need a strong element of continuous verification that proves the location and veracity of the protected area.