Avengers: Age of Ultron/WMG

All-purpose theories for characters in Avengers 2
No theory is too outlandish, nothing is out of bounds. They are, of course, all outdated, as the film came out in 2015.
 * The Silver Surfer, as mentioned below, will show up as The Cavalry when the team goes up against . They'd have to buy the rights to him from 20th Century Fox, but it wouldn't feel like a   movie without the Surfer.
 * The Vision will appear, either as an original character or as, possibly as his LMD.
 * Hank Pym and The Wasp, if only to quiet the fanboys who were angry about them not appearing in this movie.
 * Captain Mar-Vell or Ms. Marvel. Since the sequel is definitely going interplanetary, it would make sense to include the Kree as alien allies of Earth. At the very least, Carol Danvers will likely be introduced as one of the team's higher-ups at SHIELD.
 * She Hulk, if only to pad out the team's female characters, or to act as an upbeat foil for Bruce Banner.
 * Doctor Strange will introduce elements of magic into the mostly sci-fi themed Marvel Cinematic Universe, and will ultimately use a spell to help turn the tide against.
 * Disney's movie wiki states that a Doctor Strange movie is being planed. No release year is set though.
 * Black Panther will be introduced as a powerful African monarch who will become the team's ally when they (inevitably) get involved in some kind of international intrigue. Midway through, they'll discover that he's a powerful warrior in his own right.
 * Spider-Man, if The Amazing Spider Man is part of the Marvel Cinematic Universe. This is the real reason the franchise was rebooted.
 * Hasn't that one already be Jossed by Sony?

The Silver Surfer will be a major character in the sequel
I have no idea how they would iron out the legal difficulties surrounding this, but come on...it just wouldn't feel right  but without the Silver Surfer. Then again, considering Fantastic Four: Rise of the Silver Surfer wasn't exactly a resounding success, 20th Century Fox probably isn't that desperate to hold onto the movie rights to the character. If they really wanted to, the guys at Marvel Studios could probably buy the rights to him. And a role in Avengers 2 would probably be a good lead-in to a solo Silver Surfer movie (hopefully, one where Galactus isn't just a floating cloud in space).
 * I had heard that Fox was indeed trying to reboot the fantastic four. So this one looks unlikely for the near future.
 * Potentially not likely. I forget what was the reason, but Marvel couldn't use Silver Surfer in the World War Hulk animated movie. It's also possible that Fox may try to continue using the Fantastic Four license to cash in on Marvel's successes. Or they could choose to be jerks and hold onto the rights as long as possible just for spite. Wouldn't be the first time a company has secured production rights just to sit on them.

Jane Foster wasn't being protected from Loki
Jane Foster was put in protective custody to protect her from Joss Whedon. We know how he feels about happy relationships.

Director Fury's superiors...
Are the Commission on Superhuman Activities, Mark Gruenwald's famous Omniscient Council of Vagueness from the 80s Cap comics. Just 'cause.

Tony will be revealed to be a Captain America fanboy.
Possibly due to Howard telling him some old war stories about the "Star Spangled Man with a Plan".
 * Apparently, going by some interviews with the cast, it seems that Tony won't be filling this role (and then again, if the "Genius Billionaire Philantrophist" scene is any indication, we'll have a more "complex" relationship with Steve/Tony), and that will be revealed to be a huge Captain America nerd.
 * Sorta Jossed.

Hawkeye is going to betray the rest of the team about halfway through.
Only to be brought back to the side of the Avengers near the climax. I don't have much in the way of evidence, it's just a feeling I'm getting from the trailers and the released info about him.
 * Half Jossed, half confirmed.
 * Half Jossed, half confirmed.

The Big Bad of the film will be the Void.
And the plot will be as close to Siege as possible without having either Spider-Man or Norman Osborn in it. Yes, this means.
 * Jossed.

The Wasp will appear, if not in the first, in a second Avengers movie.
And her tendency, in the comics, to switch costumes a lot, each one more flamboyant than the other, will provide an excellent opportunity for an Actor Allusion. Which young female celebrity has a similarly bizarre fashion sense?
 * as Wasp? No. God, no.
 * I think they would use as Wasp.
 * You disgust me.
 * Jossed

Spider-Man will have a cameo in the film
Think about it logically. Granted, Spidey wasn't in the original line up for the Avengers...but The Avengers is out in 2012, and so is The Amazing Spider-Man; it makes sense that they ask Andrew Garfield to do a spot of filming alongside RDJ and Chris Evans; they could have Spidey act like a fanboy around Tony and Steve; Tony cause he's a technological genius, and Steve cause he's... Well Captain America (comics). He could even phone Gwen after and say "[Hey Gwen, guess what? I just met CAPTAIN AMERICA!" And for one more tip of the hat, if the Avengers takes place after the events of TASM, then Spidey could have his original red and blue costume on.
 * Wouldn't work. Marvel Studios doesn't have the rights to Spider-Man or X-Men, which kinda puts a wrench into the works.
 * X-Men First Class may or may not be in continuity with these films (they sure as hell aren't in continuity with the other X-men films), but it's not outright stated. It's possible that future Spider-Man and X-Men films will make reference to the Avengers or the the events of this film without the characters actually showing up, at least not until Marvel can get the rights to them back.
 * Jossed
 * Further jossed based on commentary from The Incredible Hulk. They had asked Sony if they could use Empire State University, but Sony declined. They also asked if they could have Spider-Man swing by in the background of a scene or just have Tobey Maguire standing in a crowd scene. Both were declined, so the likelihood of Sony connecting Amazing Spider-Man with a rival company is improbable.

The Avengers will leave S.H.I.E.L.D.

 * The events of the first movie will cause the Avengers to quit in order to work as an autonomous group.
 * Alternately, S.H.I.E.L.D. will consider the Avengers a failure for one reason or another (probably against Fury's wishes) and shut the program down, but Tony and/or Cap will basically say "You can't fire me, I quit!" and reform the group, making it operate out of a Stark-owned mansion in NYC.
 * Jossed.

Jenny Agutter's character is Peggy's daughter

 * Possibly Falsworth's, too, for maximum Britishness.
 * Jossed. She's apparently gonna play a Obstructive Bureaucrat character that's with the "World Security Council".
 * Assuming she's human, she's got to have parents. Two of them.

Steve will respond to Tony's 'Playboy Genius' boast with an armor-piercing statement

 * It'll probably be something pertaining to Tony's father, and might be a bit harsh, but fair.
 * Respond he did.


 * This does make sense, and Marvel has been pushing Ms Marvel quite hard in recent years.
 * This does make sense, and Marvel has been pushing Ms Marvel quite hard in recent years.

Agent Phil Coulson will be reborn as The Vision

 * Tony hints of a "Life Model Decoy" when Coulson tries to contact him. And considering that the Vision can change brain patterns.....

But, after the medical team arrives on scene and
 * There could be some merit to this.
 * Wait a minute now. Did we actually here the medics say it, or just Fury say that they called it?

And with SHIELD having this hi-tech helicarrier with hi-tech equipment on board, who knows what happened in the med-bay? What if Marvel is planning to bring back Agent Coulson as Vision?

It's said at least 3 times in The Avengers that Coulson was dating a cellist. Guess who's a cellist in the Marvel Universe? Wanda Maximoff aka The Scarlett Witch. And who is Scarlett Witch's husband in the comics? Vision, the human/synthetic reincarnation of a dead hero. both are Avengers.

Gregg's contract is for more films than he's been in so far, and while the original Vision was an android created by Ultron, so far Marvel hasn't been afraid to change certain details to fit the story.

Now you may be thinking, "But Fox currently holds the right to use mutants." But that isn't necessarily the complete truth. Kevin Feige brought this up at the red carpet premiere. According to him, both Marvel and Fox have rights to Scarlet Witch and Quicksilver jointly. I'm guessing the deal is that Marvel can't refer to them as 'mutants' and connect them to Magneto or the X-Men in any way, while Fox can't refer to them as being associated with The Avengers.

What's even more interesting is that he brought up those two characters specifically as characters who could appear in Avengers 2. why would he mention Scarlet Witch now? It all seems too good to be a coincidence.

''From here on, it can only be noted that talking about any possible developments in this series will have a high probability of ending in frustration. I mean, we know who's been holding the strings.


 * By SHIELD, to save his life (and have a trustworthy superhuman as a nice bonus). Or maybe having been has nasty side effects. One way or another, he'll become orange, superpowered, and eventually be instrumental to defeating . And yes, this assumes  has an, as per another WMG above.

The next move of

 * Very basic reasoning. The Tesseract can open a door to  area of space, from either end. At the end of the Avengers, both the Tesseract and   Infinity Gauntlet are sitting in Asgard, he's got an obvious motivation to get his hands on both objects, and Earth has just shown it's not an easy target, so   is unlikely to strike it again soon without his cosmic toys. What do you want to bet the plot of Thor 2 or Avengers 2 involves an invasion of Asgard by   minions?

The Sequel will feature another team of superheroes...

 * ... Nextwave, Agents of Hate. Because that'd be awesome.

In Avengers 2, Loki will be the Avengers' Hannibal Lecter
Since he's the only one who had contact with  who will probably be the Big Bad in Avengers 2, the Avengers will have to go to him for information on   and how he works. Loki will probably be his normal self around them, but might be motivated to help since the Chitauri warned him that if he failed to get them the Tesseract then they would find him and take vengeance on him.
 * Besides, giving him that mouth-gag in the custody of the original Hannibal Lecter himself is just too sweet to pass up.

Nick Fury will use a Laser Blade in the next film.
And it will be purple, mainly as a reference to Samuel L. Jackson's role as Mace Windu.

Scarlet Witch will appear in the next Avengers movie, tying it together with the X Men movies

 * She will be introduced escaping a Insane Asylum to warn SHIELD about the new movie's villian. No one will believe her so she will use her powers over chance and probability force ridiculously unlikely circumstances to bring the Avengers together at the right place and time to face the threat. She will also rant about and make references to events and people from the comic book universe including her two non-existent sons, everyone will dismisses it as mad delusions.