If the D&D movie is a success, then then 6e will be whatever is necessary to make movie fans feel like they are playing in the movie (and since it is a Hasbro movie, they will make changes).
If the movie bombs, Hasbro will sell WotC, and Mattel will buy it (cheap) so the 6e will be set in Eternia. Dark Sun will take place in the Sands of Time, Eberron will be in the Three Towers (and instead of warforged, you can play a Horde Trooper), etc. When they do expand to another world, it will be Thundera.