Bill Murray admits to Howard Stern that he hasn't read the Ghostbusters 3 script

I've sorta let the whole Ghostbusters 3 thing die out over here, mainly because I just don't feel it's worth covering. Not until the damn thing actually gets put into motion. It's just aggravating that every other week there's some new speculation: "Oh, Ernie Hudson says it's definitely happening!" "Oooh, Bill Murray was caught with a Slimer bumper sticker so it's definitely happening!"  Um, no. At this point all we have is an overly excited studio, a washed up director(who the studio didn't even want!) and some mostly washed up ex-comedic giants up for the sequel, and the one legitimate star who seems to have zero interest.  That star would of course be Bill Murray, whose intentions towards appearing in Ghostbusters 3 waxes on and off like the Karate Kid.   

Calling in to Howard Stern's satellite radio show, Murray spent a pretty hefty chunk of time explaining his hesitation about the film, and his attitude towards sequels in general.  I only just had a chance to listen to the nearly hour long discussion, and it's compelling stuff. Here is the relevant portion, transcribed for your reading pleasure.
STERN: Is it true that there is a “Ghostbusters 3” and you’re the problem? You will not sign off on this? Do you know about this?

MURRAY: Yeah, I guess I’m the problem. Before I was an asset and now I’m the problem. There’s a script somewhere over there. Over there there’s a script and I haven’t read it yet.

STERN: Why haven’t you read it? Because you think it’s a bullshit idea? In other words, Ghostbusters had its time and you did a remarkable job with that, and you’ve moved on?

MURRAY: There’s a little bit of that. You know, I only made one sequel, “Ghostbusters II,” and it didn’t end up the way it was presented. About five years after we did the first one, the clever agents got us all together in a room, and we really are funny together. I mean they are funny people - Harold and Danny and myself, and it was Ivan and maybe one or two other people. And we were just blindingly funny for about an hour or so. And the agents, there was just foam coming off of them. And so they had this pitch and Danny and Harold had already concocted some sort of story idea, and it was a story, it was a good story. I think I had even already read one or two that Danny rolled out before that, but this one was a good one. I said, "OK, we can do that one." It was just kind of fun to have all of us together. I mean Moranis, Rick Moranis and Annie Potts. These people, they’re just sterling people to begin with.

STERN: So how do you go back and really make another? Does Ivan want to make that film?

MURRAY: Yeah, Ivan wants to make it and I owe him and he’s puzzled that I haven’t gotten to this one.

STERN: How long has it been sitting on your desk, this script for Ghostbusters?

MURRAY: Well, it may not be on the desk; it’s over there somewhere. How long? I don’t know.

STERN: So you’re never going to read it.

ROBIN QUIVERS: So you have no interest.

MURRAY: Well, I’ll get to it. I gotta get to it. I feel badly. I got a message. I don’t want to hurt anyone’s feelings but it’s not the foremost thing in my mind right now, so I don’t think about it. You know what, the studio gets excited about it every 10 years or so or it seems like, and they read it. Because what they’d really like to do is recreate the franchise, you know? I remember once upon a time it was going to be, “And the new Ghostbusters will be Chris Rock, Chris Farley and Chris Crane or Kris Kringle.” Or someone. They had it together.

STERN: Is that a threat to you? In other words, do they try to threaten you by saying, “We’re going to put together a new Ghostbusters, and therefore you guys will have to go do it?”

MURRAY: It’s not a threat. It’s sort of businesslike. They’d like to keep it going. I mean, it’s still an amazing … there’s still kids today that watch this movie. They still sell a lot of toys and everything.

I think Murray makes it pretty clear that if this thing is ever going to get off the ground it'll happen on his own schedule. It was pretty funny the way he jabbed a sharp stick at all the earliest stories about the casting possibilities for the film, which featured any number of today's hot young actors donning the Ghostbuster Proton Packs.