"Ghostbusters 3" is a movie people have been wanting to see since 1989.  After "Ghostbusters 2" was released, though not a s successful and acclaimed as the original, there was still desire to see a third movie.  For the past several years, rumors have been going around about the state of a new movie.  Back in August, Dan Aykroyd talked about getting the entire cast back together and what the general story would be, but since then rumors have been circulating about Bill Murray's frustration with the project. 

According to some reports, when he received the current working script for the new film, Murray immediately ran it through his paper shredder without looking at it, saying that no one wants to see fat, old men chasing ghosts.  While doing a web chat at Empire magazine, Dan Aykroyd was asked if that story was true,

"Bill Murray is not capable of such behaviour. This is simply something that would not be in his nature. We have a deep, private personal relationship that transcends business. We communicate frequently and his position on the involvement in Ghostbusters 3 has been made clear and I respect that. But Bill has too much positive estimation of my writing skills to shred the work." 

While a statement like that makes me a little more hopeful about the project, there is still the idea that Dan Aykroyd, Harold Ramis, and Ivan Reitman would actually recast the role of Peter Venkman.  I've heard this rumor for a while now, and the interview with Empire magazine addresses it... kinda.  According to Empire, Aykroyd hinted at the possibility of another actor playing the role of Dr. Venkman, with this quote as their example,

 "The script must be perfect. We cannot release a film that is any less than that. We have more work to do."

I have no idea how they got "We will recast the role" from that.  It doesn't match up with the way Aykroyd has talked about the project in previous interviews, as well as this one.  I don't see how anyone on the project would be willing to see someone else play Murray's role, but they want to have Rick Moranis come out of retirement to do the movie,

"If we can get the script to Ghostbusters 3 right, then it would definitely have Moranis as a major component. None of us would want to do the movie without having him as a participant."

So just take the recasting ideas as pure speculation on the part of Empire magazine.  With a project like "Ghostbusters 3", its unlikely the movie would made without any of the major cast; and to a lot of fans, Bill Murray is the biggest part of the franchise.