The article was a cool read, but the area in that article isn't for theme park development. Although Disney has already outlined where it will build its 5th park (and possibly a 6th and 7th), they are committed to increasing the density of the current developments on property. However, even though many things are subject to change based on the current business climate (and political), too much has gone into the infrastructure that is already in place.
For a 5th park, I would take a close look at the current Magic Kingdom parking lot. As strange as it may seem, just take a look at disney theme park configurations all over the world, disney's infrastructure on the Florida property, and current and forecasted guest flow patterns.
I invite everyone to check out the Reedy Creek Development's online and offline plans they have posted for the future of Disney World. It's all information that the public can take a look at, digest, and run with!