I think most are probably right that it will be Kraven, Mysterio, Scorpion, or Chameleon. But that kinda disappoints me, TBH. It seems that Marvel wants to focus on characters who've not been on film before. But I mean...at some point isn't it just underwhelming to have films filled with second-tier villains. Its like making a Batman trilogy with Firefly, Mad Hatter, and Man-Bat as the villains while snubbing Joker, Penguin, Bane, Two-Face, Riddler, etc because they have been on film before. The A-list rogues are A-list for a reason and just because they have been used before, doesn't mean there is less value in seeing them on film again, with a different interpretation, and in the setting of the MCU. Because really, it would be such a missed opportunity to not have Doc Ock or Green Goblin take their place in the MCU while it is in its prime.
And for nothin', but by the time this movie is released, it will have been 15 years since Doc Ock appeared on screen and nearly 20 since we got a proper version of Norman Osborn.