Fox WAS planning to spinoff the charactr after Fantastic Four: Rise of the Silver Surfer, but now, after that movie's mediocre performance, the project is in limbo. Here is what we know from this interview:
"Whether or not it ever gets made I don't know because they were kind of disappointed in how 'Fantastic Four 2' did," Straczynski said. "And given how this will be a subset of FF2 in terms of the marketing strategy, I think there is hesitation there about putting it forward. The script is pretty good, I like it, but whether or not it goes into production, I have no idea."
The movie was to begin directly from the ending of FF2. We find out why Silver Surfer was there and what happened to him after thwarting the omnipotent planet devourer Galactus.
"We would have seen Galactus, his home world, what happened and him trying to get back there, because now that he's betrayed Galactus, he's concerned his home world might be in jeopardy."
Asked to explain how we would see Galactus, he said, "In the script I come up with some ways to visualize him that are true to the original, but take it one step further using the current CGI technology that we have. So we would have seen him as a character on numerous occasions in the second movie, not inconsistent with the first distant shot of him in that that's just a way of concealing who and what he really is. Believe me, he would be not at all silly looking."