How open will the Open Gaming Content be? What about the setting? Is this leaning more toward the "all proper nouns are Product Identity" side of things or more toward the "all text is open content" side?
I help run a shared campaign in the Pacific Northwest (mostly in Victoria this year, but it varies), and we like to visit different worlds and send PCs careening from one plane to the next. When settings (and adventures, and monsters, and whatever else) are made entirely of open content then we can just drop them in and go. Because we end up publishing recaps of events and reusing settings and the like, we have to adhere to the OGL and we can't use Product Identity.
I'm hoping that the Pathfinder and Gamemastery publications will be open to the point that we can take them and drop them into the campaign. I'm confident that they'll see more play that way. I've been disappointed that we couldn't use Dungeon adventures, and I'm hoping that this change will benefit us in a big way.
I don't think that this necessarily follows. We could see PCs who are outside the core classes in a couple of different ways.
1. Paizo could make up new classes.
2. Paizo could use classes from other d20 sources.
Granted, the adventures are the reason I'm buying Pathfinder. :) I was just saying that the fact that Paizo is using the OGL doesn't necessitate that they we never ever use anything other than core classes.