According to Cinema Blend on Thursday, the release of "The Amazing Spider-Man 2" on Blu-ray gave rise to extra bonus scenes to commentary that revealed and confirmed the next three members of the Sinister Six. There was also talks of Harry Osborn's father, Norman Osborn, played by Chris Cooper, that reveals the mechanism by which his head is being cryogenically frozen.
That being said and with plans on the director partaking in the return of Norman Osborn, this could be made analogous with The Joker arch rival's Batman. After all, Norman Osborn, at least in the comic books, is the "meat and potatoes" villain when it comes to the web slinging rival that he has always been adversarial towards. He didn't have much of a part in the movie, but it would be nice to see him move forward and have a larger role in the franchise.
For those who had scene the silhouette of a man in the shadows at the end of "The Amazing Spider-Man 2", director Marc Webb deemed him The Gentleman that is the benefactor of the Sinister Six. Also, in the Blu-ray commentary, there had been objects or technology teased even in the movie.
One of them that looks to be the mask of Mysterio and the other the spear of the likely Kraven the Hunter. Some of these pieces had already been on display at Oscorp in the movie and now some of this technology seems to tie into additional villains of the Sinister Six.
That being said, director Webb is hoping to see Kraven in the film, but with "The Amazing Spider-Man 2" having done sub-par in the box office, Sony Pictures will indeed to perk up to get comic book fans excited about this continuing franchise.