I don't come to this area of the board much - and you all probably know this already - but the treehouses couldn't be used anymore for the general public because of not being ADA (handicap) accessible. The captain of the boat taking us to DTD from POFQ told us that, and that they were used for the college program housing, at least they were at the time he told us that. So, if they wanted to actually use them for any reason, I would imagine nothing short of rebuilding them would work, or they would have already made the changes a while ago.
I bet it drives the "powers that be" at Disney to have those there and not be able to use them. They are so unique that it is probably a good investment.