First things first this isn't a fan cast, its not a theory either it's just an idea that really sticks in my mind.
A heist film... about someone who cant be caught.
And by this i mean can't be recognized. I've always liked heist films, there's something about the elegance and the confidence of the characters that glues me to the screen all through.
I think a film like this featuring the Chameleon (Dmitri Smerdyakov) would be great, for the simple reason that he could go in and out several times without being discovered.
My main idea for the story is this:
After a pattern is found between people emptying their bank accounts suddenly and having no recollection, a team is put together to see if they actually were the people taking the money. This search sparks an interest in Natasha Romanov (I'm working outside of rights here) who recognizes the M/O to be Chameleons from her experience with him. (shown in the ends of the earth Spidey story arc)
So anyway, the chase goes on and Black Widow contacts Chameleon and tries to blackmail him with secrets he has kept from his own family. As a result of this he decides to pull off a massive score before the net closes in too tightly: he decides to break into Avengers tower.
At this point cue a montage of preparation for both Dmitri and the team, led by Natasha and skip to the heist day, a week later, Chameleon plans to pose as Tony stark and access his armory to sell arms, we see him get in then cut to the team, they discover he's there and use a method of deducton to find out who he is posing as, finding out the moniker he is using, they have the building put on lockdown and initiate a manhunt for "Tony". believing to have found him they open the door to the armory and find him tied up with a note: "Thanks for the nest egg, wont see you later!" At this they try to figure out what he did in vain and in the end we see D'mitri on a tropical islands, sipping a cocktail. Typical ending right?
Obviously the guys at marvel will have a suprise, perhaps a baron approaches him for a team? I'll leave it to you.