Well, I'm no insider, but yesterday I had been yearning for the same thing, and started making a crude marking-up of all of the future/possible expansion plots that aren't already inhabited by some attraction or venue of significance. So, the white areas are the ones that could be used for future expansions, with the exception of the watercolor lines (I used Paint) that could be future monorail/other transportation routes; the green outlines could be resorts; the first kidney bean-shaped outline can be another CityWalk, and the two oval-ish shapes can be new parks; the the blue outlines represent possible artificial bodies of water; the area where Cabana Bay Beach Resort is going is greyed-out because Google Earth didn't have a recent enough picture for it to be there at all. Maybe we can work from here?
Of course, this is completely from my own imagination and I have no idea what it may actually be like, but at least this way one can begin to visualize all the different expansions and their relative sizes and such (or laugh at my shameful attempt at creating a visual aid for something)
Oh, and can someone tell me if the picture I included actually shows up? On my ipad it just shows the infamous blue question mark box...