It's a bit early for a write-up like this, but since a majority of the international markets are getting the film early. I decided to get his out of the way. I'm sure I missed a bunch of tidbits that were teased in Amazing Spider-Man 2. However, I have a few theories and ideas of where the third installment could be going. I'm not reviewing the film, but there are major plot SPOILERS contained in the explanations. You've been been warned!
SINISTER SIX: While it was assumed that Electro was going to be one of the six members, Max doesn't make it out alive. His return isn't very likely, and I assume that Dr. Curt Connors/The Lizard will be reluctant to join the villainous team. At the end of the first film we see Curt pleading the shadowy figure to leave Peter allow, I doubt they'll be able to convince him to kill Spider-Man.
It looks like Harry Osborn and his shadowy friend are using "willing" hired guns to operate the Oscorp tech. Breaking Aleksei Mikhailovich Sytsevich out of prison to operate the Rhino mech-suit, at the end of the movie. Considering a majority of the tech is robotics, I'm starting to believe that this shadowy man might be in fact Dr. Spencer Smythe. A notorious robotics engineer who has a grudge against Spider-Man, creating the Spider Slayers. His son Alistair has already been revealed as working for Oscorp and is played by B.J. Novac. Currently, the Sinister Six lineup includes Goblin, Doc Ock, Vulture and The Rhino. I won't rule out The Lizard entirely, but it's possible from the poor reception of the character, they might not bring him back.
FELICIA HARDY/BLACK CAT: It's revealed that indeed Felicity Jones is playing Felicia Hardy, and works for Oscorp as an assistant to Norman Osborn. It's unknown where her loyalties lay, but starting her off as a villain wouldn't be hard to see. Hardy's father was a famous cat bugler, who worked for Wilson "Kingpin" Fisk. Felicia would eventually take a position at Fisk Enterprises, something that was mirrored with her employment at Oscorp. Considering that Mary Jane Watson might not even be featured in Amazing Spider-Man 3, originally played by Shailene Woodley (completed cut-out of the films and eventually recast). It's possible we could see Parker and Hardy become an item, before Mary Jane enters the picture. This wouldn't be going against the comics, since Black Cat and Spider-Man did briefly date.
Black Cat is the type of Spidey character the franchise needs. Considering we've never had a female villain in the franchise. And we know that Sam Raimi had originally intended to use the Black Cat (played by Anne Hathaway) in his never-filmed Spider-Man 4. Female characters are rare in this franchise, let alone ones that play both villain and hero. If Sony is looking for spin-offs a Black Cat film could be spot-on. Producers have been talking non-traditional lineups for the Sinister Six, adding a female character like Hardy into the mix would mess with the boys-only supervillain group.
DR. ALISTAIR SMYTHE/SPIDER SLAYER: B.J. Novac is revealed to be Dr. Alistair Smythe in the film, and is the son of notorious villain Spencer Smythe (possible identity of the shadowy figure), who invents the Spider Slayers. These are group of robots who are programmed to hunt, capture and or kill Spider-Man. Alistair himself is turned into one of these Slayers, as he's eventually becomes a cyborg. I'm not sure that's a route they'll want to go, but that door is a possibility. I still think that Spencer is the one who built, the Vulture wings and Ock's arms. Basically, becoming an evil version of Lucius Fox, providing all the robotics and bio-tech weapons he needs. Smythe could fall into the realm of an untraditional member of the Sinister Six, if they go that way. It's very possible he could end-up becoming the new Doctor Octopus.
MACDONALD GARGAN/SCORPION/VENOM: The Venom symbiote has been revealed to be an Oscorp experiment, and could easily join the ranks of The Sinister Six. It's possible we could see a new origin of Venom, but since he's getting his own spin-off movie, that could be saved for another film. The producers haven't actually revealed which host Venom will be using, my assumption is that they could end up using either MacDonald Gargan or Flash Thompson. The Gargan version of Venom worked for Norman Osborn's Dark Avengers, which could be another untraditional Sinister Six member. Plus, Mac has a long history fighting against Spider-Man as the villain Scorpion.
Having Mac start out in the Scorpion suit then having his ass handed to him by Spidey. Could fuel his anger to go a little more extreme than the other members, by bonding with the Venom symboite. At the end of the film seeing the government using it for their own means, with Flash Thompson as the host could be the way to go. Flash taking the more heroic role of Venom, recently in the comics. It's less likely we'll see the return of Eddie Brock, since that version has already been done by Raimi. Marc Webb and Sony have been seemingly trying to reinvent the villains, so not using Brock as Venom might be a good creative move. Since characters like Gargan and Thompson (a disabled veteran turned superhero) have stronger stories and arcs than Eddie.
SERGEI KRAVINOFF/KRAVEN THE HUNTER: We're starting to see that some characters from the video game tie-ins are making their way into the sequels. Felicia Hardy and Alistair Smythe were featured characters in The Amazing Spider-Man Game, and would eventually have small roles in Amazing Spider-Man 2. It's plausible to think that The Amazing Spider-Man 2 Game, could have a similar trend. In the new game we see notorious Spidey villain Kraven The Hunter, playing mentor rather than antagonist. Parker is going to need his own team-mates, if he's going up against The Sinister Six. Kraven might have been originally a member of the Six, but we've heard from producers the lineup won't be entirely traditional.
In the Ultimate comics (which the new movies are sort of based on), Sergei is an Australian (rather than Russian) reality TV host. Who wants to hunt and kill Spider-Man live on television to boost his ratings. His family has many links to Spider-Man as well his half-brother just happens to be spy for hire and master of disguise, Dmitri Smerdyakov better known as The Chameleon. His offspring (which includes two sons and a daughter) also took up his mantle. If we do see Kraven, the writers could make him friend or foe. Sergei is one of the most popular Spidey characters, and it's shocking they haven't used him in the movies.
WILSON FISK/KINGPIN: Like Kraven, Wilson Fisk of Fisk Enterprises is featured heavily in the new video game. In the game Fisk and Oscorp start to work together, in some sort of merger. Marvel's Kevin Feige has revealed that they share the Kingpin rights, as the villain is equally known as a Spider-Man baddie as he is a Daredevil villain. We've seen Oscorp take-up a majority of threat for the city, but it would be interesting to see Osborn working alongside Fisk. Organized crime has always been apart of the Spider-Man comics, and not including that might change in the future. Fisk could have employed people like Aleksei Mikhailovich Sytsevich (The Rhino), Herman Schultz (Shocker), Lonnie Thompson Lincoln (Tombstone) and crime lord rival Hammerhead.
Fisk is also the reason Felicia Hardy gets her Black Cat powers, and the two might be tied-together (at one point Felicia works for Wilson), if Sony wants to eventually turn Hardy into Black Cat. Although, they've been messing around with origins lately, so changing Black Cat's origins as well wouldn't be surprising.
DR. MICHAEL MORBIUS: I'm not entirely sure if the Easter Egg with Morbius in the film was nothing more than just that, a tease. I haven't actually seen anything that suggests that, Sony has the rights to use Morbius in their films (as a vampire, he could be directly connected with Blade movie rights, which included all Marvel vampire characters) and have the intention to do so if they did. Showing up at the end of the original Blade film (in an alternate ending), could mean the character is either at Marvel Studios or shared with Sony (Kevin Feige hasn't confirmed this). He is a cool and complex character, that has spin-off potential and would make a cool team-up parter for Parker. I'm sure Marvel Studios would want to use Morbius, if they ever put together Midnight Sons or Legion of Monsters movies.
It's also established that since the Connors innocent, they've scrapped the animal divisions at Oscorp, so it's unknown if Michael is even still doing research at the company. This suggests we'll see less animal-spliced (Eels/Electro and Lizard/Connors) characters in future films. That could exclude Morbius and his bat experiments, that led him to turn himself into living vampiric creature.