The story says Fox has committed to "combine the Fantastic Four and the X-Men for an "Avengers"-style movie that could pay off huge for shareholders." Earlier this month Simon Kinberg took on the job of merging the two universes into one, and consultant Mark Millar has said in the past that the X-men and upcoming Fantastic Four reboot will take place in the same continuity.
So perhaps this is just the logical extension of what we already knew, and Motley Fool is simply voicing what they think will happen. Or are they simply revealing what has already been shared with the people who control the money? The story does get into some specifics, though, saying the plotline will be based on the 1987 crossover that saw both teams fighting to save the life of Kitty Pryde. Secrets arise regarding the origin of the Fantastic Four and Reed Richards' true part to play in it. Doctor Doom is in the mix, as well, doing his best to sew dissension between them . I remember thinking this story was needlessly convoluted even back then, and think there's little real chance it could be used in a movie without drastic changes.
We'll see what happens, but we know Fox would be down for making this movie a reality at some point. If X-men: Days of Future Past and its sequel 'Apocalypse' do well, and Josh Trank's Fantastic Four relaunch takes off in 2015 then it's probably only a matter of time.