I could definitely see them being risk averse enough to wait until summer 2016, that's a very fair point. By then Episode VII will have been in theaters since December and it's impact will be crystal clear.
My own personal feeling is that it's going to hit like an Atom Bomb. It's a perfect storm for a box-office mega-hit. If Disney can market and promote mediocre and forgettable films like PIRATES OF THE CARIBBEAN: ON STRANGER TIDES and ALICE IN WONDERLAND to over a billion world-wide box-office, then the very long awaited sequel to the most popular movie series in the history of cinema should do mind blowing numbers.
If it's insanely huge they'd be crazy not to take advantage of it. I heard the term "Potter Swatter" in another thread, and that sounds pretty apropos. Walt Disney World wants guests to stay on property, making Disney's Animal Kingdom and Disney's Hollywood Studios legit full day parks by adding Avatar Land and Star Wars Land respectively is a great way to do it.