In an interview with Vanity Fair, Dan Aykroyd revealed that he is currently working on the script to Ghostbusters III:
Speaking of your film career, last month in GQ Bill Murray said something that wasn’t so nice about Ghostbusters 3.
He was talking about the writers from Year One, and I think he was reacting to the box-office success and the general public view of the film, which in my view was a very serviceable comedy, and in the end I think they’ll make their money back. I think he was concerned that the writing on Ghostbusters 3 by these guys would not be up to standard, but I can tell you firsthand, I’m working on the script now and those two—Stupnitsky and Eisenberg, [writer-producers of The Office]—wrote Bill the comic role of a lifetime, and the new Ghostbusters and the old are all well represented in it…we have a strong first draft that Harold [Ramis] and I will take back, and I’m very excited about working on it.