To be clear, I don't really believe this rumor (yet). But it does come from Bleeding Cool, which is usually a good source (there's a hearty update, however, at the ned of this article that sort of explains what these rumors are really about).
Specifically, the rumor comes from Rich Johnston, who claims that sources from within the film's production are calling for reshoots and maybe even new talent. He even quotes an anonymous executive as saying it's "a mess" and that sets in Louisiana might be rebuilt.
Personally, I think people just want to hate this movie (not that they haven't already) and are jumping at any rumor they can to discredit it. Johnston even admits that he's been fed negative comments about the movie since last year, including claims that Fox wanted to hire new writers.
This may have nothing to do with these rumors, but you have to figure Johnston has gotten a little biased at this point.
That, or he's still smarting from the last one of these movies.
He even dismisses a recent, positive comment made by one of the producers, Matthew Vaughn (X-Men: First Class), by saying F4 will fail for trying to be Chronicle 2. Maybe I'm overstating, but that seems a little too harsh for expecting a movie to be as good as Josh Trank's last project.
And you have to feel bad for Fox, who's in the uncomfortable position of having to market a film people are going to lash out at no matter what they do at this point because it's not in the sacred cow that is the MCU, even though this movie failing will NOT lead to Fox giving up Fantastic Four (it's just not going to happen).
More importantly, I feel for the fans who are genuinely excited about this movie, but they can't say anything about it because they'll get chewed out for not hating a movie we haven't even seen a trailer for yet.
Until then, this is what the critics look like...
Are you still hopeful for the Fantastic Four reboot as-is?
UPDATE: Badass Digest claims that the reshoots are only for adding action scenes to a character-driven story, not because the movie needs to be retooled completely. And Josh Trank hasn't been ousted as director. Apparently, these rumors have been surfacing because the film is balancing being a origin movie that doesn't show them as "The Fantastic Four" until the very end, so they're not sure which way they're going to market the film yet.
UPDATE: Admittedly, I was a little harsh with Rich Johnston. As he put it in the comments below, he's just passing on information, and I misinterpreted.
Source: Bleeding Cool