A lot of people still feel it's never going to actually happen, and Bill Murray has referred to it as a myth, but development is still pressing ahead on Ghostbusters 3. However as everything's been moving at a snail's pace, it's only added to the feeling that it'll never get in front of the camera.
Indeed, Bill Murray's assertions that he doesn't believe it'll go ahead (and it's dependent on him saying yes, as most of the original actors have a vito on further sequels), as well as various comments denigrating the talents of the writers of the first draft of the screenplay, Gene Stupnitsky and Lee Eisenberg, have pretty much suggested Murray is just waiting to say no.
However now it appears Dan Aykroyd and Harold Ramis have stepped into the breach and are taking over writing of the Ghostbusters 3 screenplay. While promoting his Vodka brand, Aykroyd told Vanity Fair that "I think [Bill Murray] 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 - 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."
On the plot, he added that, "Now [in Ghostbusters 3] my character’s eyesight is shot, I got a bad knee, a bad hip - I can’t drive that caddy anymore or lift that Psychotron Accelerator anymore, it’s too heavy. We need young legs, new minds - new Ghostbusters; so I’m in essence passing the torch to the new regime, and you know what? That’s totally okay with me."
So will it happen? Will is actually get made? It's still too early to say, especially as Sony is known to want someone other than Ivan Reitman to direct, but he's also got a vito that allows him first shot at the directing gig, and the studio can't sack him without his own, and the rest of the Ghostbusters, permission.