Possible spoilers for The Amazing Spider-Man 2
Near the end of the movie, we saw Harry at the Ravencroft Institute, where said he wanted to get a gang together. He said that he needed a small number (6, like in sinister six is small). He said that all they need is already at Oscorp Then, when we see the secret projects at Oscorp, we see the wings of Vulture, the tentacles of Dr. Octopus, and Rhino's costume. All these along with Electro, have been in Sinister Six.
Could this mean that this movie hinted a Sinister Six movie?