FWIW, drowning hint or no, they've GOT to bring Alfred Molina back for future Spidey flicks. It ain't Spidey without Doc Ock, and he was great in the role. Besides, the only top-tier Spidey villain left now is The Kingpin -- who hires other supervillains for muscle.
There are lots of second-tier villains left of course, most notably Hobgoblin. I know they've gotta do that at some point, after all we've got obsessive underachiever Harry Osborne having visions of his late dad ... but really, is anybody interested?
FWIW, in the comic, after Harry got himself killed as Hobgoblin, the original Green Goblin literally rose from the grave, found out his son's fate, and said, "Wow, Harry, you always were a disappointment."
Man, that Norman Osborne is harsh!
PS: In other news, kelloggs2066 informs me that they found Ice on Tattooine!