Lucas was seen surveying the park years before he sold Lucasfilm. So I have always assumed one of the selling points was Disney committing to some sort of SWL for his legacy. Probably just back of the napkin sketches at that point but I think the ball was rolling* well before 2011.Iger originally announced Pandora in 2011. Lucasfilm wasn't acquired until 2012.
*not an IJ pun.