Nolanization strikes again! Christopher Nolan is why we can't have nice things. Yes, the actual reasons are infinitely more complex, but I'm just going to take the cheap and easy way out and blame Nolan.
If they wanted a "grim 'n gritty" Fantastic Four film, why not work with the premise from the Marvel limited series Ruins? In that world, absolutely nothing went right at all, and the FF died when they came back to Earth. Reed was horribly distorted and his heart gave out, Johnny burned without being able to protect himself from it, and Sue couldn't see because light passed through her eyes...so she fell on top of still-burning Johnny. The only survivor was Ben Grimm, because he'd been unable to make the trip for reasons that escape me.
So, yeah, there's a grim 'n gritty film right there. A hideous tragedy befalls three great minds, and the Earth has to deal with it. With just a smidge more connection to the IP, you have a non-superhero superhero-related movie.
Or, alternately, license The Four from Planetary. That's got enough grimdark in it to make Quentin Tarantino let fly with a man squee of pure juvenile delight.
OT: hyperbole aside, the commentary being released here doesn't bode well at all. Now that we've had several superhero films under our collective belts that were respectful of the source material while still being watchable, I'm not sure how the total re-imagining is going to play out. It's a wait-and-see game, but this fills me with less confidence than Batman v Superman v the law firm of Howard, Fine, and Howard LLC.