Ghostbusters 3 might actually be a possibility as some updates to filming and the cast have hit the net.
According to the NBC affiliate WKYC, a Sony executive has named Cleveland as a potential location to shoot Ghostbusters 3 with mention that filming is to begin in 2014.
The other update comes in the form of a rumor that Emma Stone and Jonah Hill are attached. The website Schmoes Know says the two have been offered the parts of Jeremy and Anna, respectively. Stone and Hill were featured together in Superbad.
Regarding the return of Bill Murray, while it still may be up in the air it seems unlikely. Previously Dan Aykroyd said they would move on without Murray and even offered Ghostbusters 3 could be a "passing the torch" type of movie.
Bear in mind lots of comments and speculation has surrounded Ghostbusters 3 for years, but with two new mentions coming in a matter of days it has to be looked at as a good sign.