Unfortunately I can't say, which I know sounds like the most cornball nonsense ever on the internet, but it's the best I can do...
Anyway, I was actually really, really surprised by it. I had no idea it would be that much of an effect. And I can't even guess how Disney will decide to respond (or not). Obviously Avatar is the first salvo, and NGE will be an attempt to re-ensnare folks. I just can't predict whether that'll be successful. Potter is a draw, and more Potter is going to be more of a draw. If they ever build a Potter-themed hotel (no idea if this is a possibility or not)... lordy.
I think 74 is right. Once people get out of their rut and become accustomed to leaving property it could open the doors to many things. Legoland, Seaworld, KSC...
The only real problem is if you want to spend a 6th day at Disney, it's like $5 or something. If you want to spent that 6th day at Universal, it's $80. That's a hard barrier to overcome for the outsiders.