The Epcot and AK land you refer to is conservation land. Disney could build on if they really want to, but they are going to shy away from major development on conservation land if they can at all avoid it. As for DHS, west of World Drive if partially conservation, and a big part of the buildable land has been taken up by the new fireworks launch and storm water retention pond. Yes, they could be relocated but it's a strike against expanding in that direction. There is a big chuck of suitable land between DHS and ESPN, but that would have hard to connect to the DHS infrastructure.