I've been reading some of the old Lee/Kirby stuff, so I had an idea for a Fantastic Four reboot film gradually take shape in my mind, which I thought I'd share here.
(I'm assuming that Namor is one of the characters both Fox and Marvel are able to access...)
FANTASTIC FOUR: THE SUB-MARINER'S REVENGE
The film begins with the Fantastic Four already established as a team. There's a series of graphics with 3D animation explaining the Fantastic Four's classic origin as the opening credits play out (the four attempt a trip to Mars in an experimental new space-craft, are affected by cosmic rays, crash-land on earth, develop their powers, and decide to fight the good fight as a team). The graphics are then revealed to be part of a show celebrating the third anniversary of the FF's fateful space flight, and we see the FF appear on stage at a ceremony in New York City. Some of the FF's great victories over the last three years are alluded too/graphically depicted-such as their defeat of the Mole Man, Dr. Doom and the invasion of the Skrulls. The FF are clearly enjoying their lives as celebrity adventurers/superheroes. We get to see glimpses of their daily lives in the Baxter Building-Reed's scientific experiments, Sue's attempts to attract Reed's attentions and get him to commit to their relationship (they aren't married yet in this version), Johnny's playboy lifestyle, and Ben's relationship with Alicia.
We see a hobo with a beard and ragged clothes wandering the streets. He catches the news reports about the FF ceremony and this seems to trigger memories of his past, as he has vague flashbacks of the Fantastic Four at sea. He gets into a brawl with some criminals being pursued by cops and demonstrates his superior strength and agility. This leads to the FF being called in to subdue this new threat. During the battle, the Human Torch severely burns the hobo, who appears to be weakened by the heat. Much of his clothing, and his facial hair is singed off...but he manages to escape.
Later, Mr. Fantastic is analyzing footage of their battle, as he feels the hobo (without his beard) looked familiar. He believes that its possible that their unknown adversary was the legendary figure 'Namor - the Sub-Mariner'-an urban myth dating back to WW2, believed to be from the undersea kingdom of Atlantis...though there is little documentary evidence to prove he exists. In the meantime, the hobo, his flashbacks of the FF intensifying, is instinctively driven to dive into the ocean. Fully submerged in the water, he remembers his past and his true identity as Namor. In particular, he recalls how, nearly three years ago, there was a battle aboard a nuclear warship, with the then-inexperienced Fantastic Four battling a group of terrorist hijackers. Namor was observing the battle from afar, not yet prepared to intervene...and while the FF defeated the terrorists, the battle caused catastrophic damage to the ship, and some of the nuclear warheads sank into the sea and exploded. The shock waves of the blast hit Namor, causing him to become comatose, such that when he was washed onto the shores of the US, he awoke as an amnesiac and became a drifter. Namor returns to Atlantis only to find it a ruins owing to the nuclear blast. This angers Namor, who decides to declare war on humanity.
Namor manages to find a mystical horn that allows him to resurrect sea monsters to attack New York. He also finds some of the survivors of the blast, who accept him as their ruler and form themselves into an army, salvaging advanced Atlantean weapons technology. Namor and the Atlanteans thus declare war on the surface world. Namor blames the surface world for bringing nuclear weapons onto the sea, and the FF for being the immediate triggers of Atlantis' destruction.
The Fantastic Four find themselves outmatched during the initial battle, and Sue ends up being kidnapped. Namor takes a liking to Sue and tells her his story and the unwitting responsibility of the FF in the destruction of his kingdom. Sue begins to fall under Namor's spell and feel sympathetic towards him. In the meantime, the FF devise a plan to attack Namor's underwater base and rescue Sue, with Mr. Fantastic finding a way to disable Namor's enchanted horn and cause him to lose control over his sea monsters. He also defeats the Atlantean soldiers using a super-sonic weapon that affects them owing to their enhanced senses. The FF are on the verge of completely defeating Namor and taking him prisoner, but Sue intervenes and tells them the whole story, convincing them to let him escape as they are all responsible for his plight. Namor flees, torn between his hatred of humanity, his love for Sue and the mercy the FF have shown him.