Harry will undoubtedly be either Green Goblin 2 or Hobgoblin, regardless of the specific nature of the comics. Remember, Mary Jane in the movies is a condensation of MJ and Gwen Stacey into one character. It won't be a total robbery if Harry becomes Hobgoblin, except to the literal purist.

Ziskin did indeed tell Sam Raimi to "Wrap it up" in Movie 3. I doubt we'll see a movie 4 with the same cast because everybody will ask for too much money. Especially Kirsten, who is too sold on herself as an actress these days. Halle Berry was in that mode for a while. Then Catwoman happened, and suddenly she was more than happy to reprise her role as Storm. Maybe Kirsten will get that same slap in the face and will come back for a fourth film.

Or maybe they'll kill her off.