Willem DaFoe, who played Norman Osborn a.k.a. The Green Goblin in Sam Raimi's Spider-Man, and who had brief cameos in both of the sequels, apparently isn't closed to the possibility of appearing in the fourth Spider-Man movie, if it would be fun to do. DaFoe revealed the news to iF Magazine while being interviewed about his latest film, Anamorph.
When asked if he would be willing to reprise his role, DaFoe responded:
[Laughs] I had to think back to what I did on all three. It would depend on a lot of things not just on schedules that stuff can get worked out. It would depend on who is involved and what they want me to do. I feel like I was slowly exiting. The first one was fun to do, the second one there wasn't much to do, but I did it because I like Sam [Raimi], and then in the third one I was a shadow. I can't imagine unless there was something to do like a resurrection that they did in the comic book that would be fun to do. Never say never though!
While not exactly a solid "yes", it does seem like DaFoe would be open to the possibility. The real question is whether or not fans and the filmmaker want to continue the Goblin saga on into a fourth Spider-Man film.