I would love to see Otto again, and he kind of completes the team as the perfect leader, but I'm not crossing my fingers for a re-address of a well done previous villain.
Venom I can see. But Ock was really good in 2, so it may seem unnecessary to them. Then again, if he had the role he had in the Spectacular cartoon, it would slide together nicely.
What I am expecting is Rhino to be leashed, Lizard to be blackmailed or conned or something, and Electro to be either given reason to turn on Spidey or also be blackmailed/conned. To me, those three are a given.
I also think Norman Osborn will serve as this series' Kingpin, which is fine by me.
As for the other three.. personally, I think Mysterio works better solo, so I wouldn't go with him. Same for Venom - although Venom is being teased, so who knows? They'd have to rush the black suit, and I don't really like Venom out of the context of being a lone stalker sort of deal... so, still saying 'no'.
Scorpion is a strong possibility given the theme set up by the first film with Lizard and Spidey, and now probably Rhino. Oscorp is going to be trying to weaponize the concept, and certainly create a tamable anti-Spider-Man. This could easily apply to Vulture as well.
So, to me, the likeliest candidates are: Rhino, Electro, Lizard, Scorpion, Vulture.
Aaaannd I'm going to actually come back around and say Doc Ock.
I don't think Hobgoblin is very likely, unless it's a traitorous sort of scheme. Hobby would be after Osborn/Kingpin's throne. He's a usurper.