They are still there but not currently being rented out. Since the property formerly known as The Disney Institute is becoming a DVC resort (Disney's Saratoga Springs Resort and Spa) there has been some speculation that they may be incorporated into the DVC program. Again, this is speculation and since the treehouses do not fit the description of any DVC room categories it is just as likely not to happen. Others have said that they may end up being rented out for cash once the new resort is complete but that, too, is speculation.
So, for now, they sit empty.