Interesting question. I never considered if they would charge a premium for the large screen. I'd hope not but it's probably a possibility.
I think it depends on if they keep the old screen size as well. That model would keep the same price, and the bigger screen could be priced higher.
Apple has been feeling the heat over dropping profit margins. A large screen choice at a premium (okay, an extra premium) price might be just the ticket to make Wall Street happy again.
Or... Apple could keep the big screen at the same price and drop the regular model's price to better penetrate the lower price markets. Doesn't feel like something Apple would do, though.
Thoughts?