I just don't see why Disney would risk it if the film does not perform as well as expected. It is not as if they need it tomorrow, they really have all the time in the world. You would think they would be more cautious based on their recent movie projects. The whole thing could be designed and contracts prepared but the decision to actually move dirt probably won't happen until 2015, 2 years away. The earliest it would open then is in 2018-2020. If interest in the movie is not as high as expected then Disney would look into other options.
Like you said, how would they know how the public would react to the project in 5 years? They probably would rather ensure that thereis still interest in Star Wars rather than come to find it isn't as popular as they thought.
In reality though there has been no indication by Disney that Star Wars is even coming (just fans looking for reasons for it to happen). Al Lutz has been losing his credibility lately. Maybe he hears these proposals being thrown around WDI but in reality none of them have really been backed by corporate, other than Avatar.