So I guess they are limiting each sequel to just one villain? That doesn't have to be the case, and just an FYI, they haven't exactly been following the comic books thus far. Even close actually.
Personally, I hope they skip green goblin 2. I mean, one is enough . At the beginning of Spiderman 3, just show Spiderman defeating him in the teaser, then move on to the next guy for the movie propper.
I agree, a second Green Goblin isn't going to interest me. His attacks weren't even that cool, and so much more can be done with all the other enemies Spidey has.