CBR has
an interview with Jonathan Hickman on Fantastic Four #600 (Note: very major spoilers)
But there's also a promising non-spoilery quote about the future of the FF spin-off:
Once "Forever" and "All Hope Lies in Doom" wrap up Hickman will use the "FF" title to explore the characters and concepts of the larger Fantastic Four universe. "Often it will be about the kids. Sometimes it will be about everybody in the family; the legion of Fantastic Four characters. Some months it will be about Doctor Doom. Some months it might be about the Inhumans," Hickman explained. "And then, some months, it will be about other things that readers don't know about yet. So it's definitely a very interesting vehicle for a lot of the cool concepts surrounding the FF."