“Over the past ten years, I’ve thought of a whole bunch of stories that I would like to write, stories in all different genres. Last I’ve looked, I have between twenty to thirty completely new books all plotted out. I’m pretty sure that I’m going to tackle science fiction next, but who knows? In the long term, though, I definitely intend to return to Eragon’s world and write a fifth book. After spending so long with the world and the characters of the Inheritance Cycle, I can’t bring myself to walk away from them for the rest of my life.”
IMO the last book Inheritance was awful, really, really bad. The series dragged on too long, and it appeared unorganized. I guess I wouldn't mind if he wrote another book but I wouldn't say I'm excited for it.