The Hollywood Reporter’s Heat Vision Newsletter:

In 2010, according to our secret sources, Fox considered building toward a crossover movie that would have pitted the X-Men against the Fantastic Four (think of it as a Civil War for the Fox/Marvel characters). The studio enlisted First Class screenwriters Ashley Edward Miller and Zack Stentz to pen the script, which saw Johnny Storm go nova while trying to apprehend the villain Molecule Man. Johnny blows a hole in Manhattan and sparks the superhero registration act in response to the carnage.

The heroes are split on opposing sides, and among the key matchups was a Wolverine vs. Mr. Fantastic battle that ended with Reed Richards pinning Wolverine down, extending his hands until they're one molecule wide, and using them as scissors to cut the mutant's arms off (!!!). Eventually the heroes make peace … leading to a post-credits scene that teases what's next: A Skrull invasion.

…

The Fox Civil War movie was not the only crossover the studio considered. It also commissioned a treatment from superstar comics writer Warren Ellis for a different X-Men vs. Fantastic Four movie.

Crazy to think “What If", but given how the post Days of Future Past X-Men movies and F4ntastic turned out, probably for the best.

I’d give my left foot to read the Ellis treatment, though.