We had a thread on the Marvel Board where I said similar things to what I'll say here.
How would you bring the FF into the Marvel Cinematic Universe?
My goal would be to succeed big time at the box office while staying true to what I think the essence of the FF is. The powers and the look and personality of each character would match the comics, as would the relationships between the characters. I would only change the headquarters address.
In the comics, the FF were the first Marvel Age heroes. All the other Marvel Age heroes came into publication in the FF's shadow. However, in the MCU the exact opposite is true. The FF would be the newest heroes. Sure, the movies could try to pull a Sentry scenario and act like the FF were really the first heroes but nobody remembers because magic. What would be the point, though? Everybody knows we've had all these MCU movies with never a hint of the FF.
Does something important change when the FF are the newest instead of the first heroes? I think so, yes. As the newest heroes, they'll be compared to the heroes who already exist. The Thing is super strong? Sure, but so is the Hulk, and Thor as well, and to a somewhat lesser extent, Iron Man. The Invisible Woman can turn invisible and cast force fields? Sure, but Doctor Strange can too. He does it differently but he does it. The Human Torch shoots fire? Sure, but if Iron Man wanted to, he could. Mister Fantastic stretches? OK, that's pretty unique, but how powerful does that really make him? He's also a super-genius, but Tony Stark and Bruce Banner are too.
But now suppose the FF were in a different environment entirely from the Avengers. Suppose they didn't live in the Baxter Building. Suppose instead they lived in a spaceship like the Guardians of the Galaxy! This changes everything, I think. Take them out of the Avengers lane and put them in the Guardians of the Galaxy lane. Doesn't this seem like a path they could have chosen? Challengers of the Unknown with powers and loving relationships and a female member. Isn't this who they really are?
Thing is, they can still encounter pretty much all of their classic villains, just not on Earth. Doctor Doom could be a galactic conqueror. (After all, Doom was the obvious inspiration for Darth Vader.) The Mole Man could rule the underworld on any planet. The Skrulls could of course appear anywhere in the galaxy. The Frightful Four could be space pirates. (The Black Panther, the Inhumans, and the Sub-Mariner will have their own cinematic realities without the FF.) Galactus eats worlds all across the galaxy. The Impossible Man could pop up anywhere. The Negative Zone could threaten the whole galaxy (as it did in the Annihilation mini-series).
I think this is the way to go. What do you think?