I think Dan Aykroyd needs to take the hint that Bill Murray simply does not want to do another Ghostbusters movie!  Bill has made it clear that he is not interested and wants nothing to do with another edition of the movie, and I think this last little stunt he pulled may have finally got the message across.

You see, Dan Aykroyd and Harold Ramis have been working on a script for Ghostbusters 3, because Dan wants to butcher it just like he did Blues Brothers. They sent the script to Bill Murray who according to the Enquirer, shredded it and mailed it back to them with a note saying "No one wants to pay money to see fat, old men chasing ghosts."

With this coming from the National Enquirer, it may or may not be true, but again Bill has already said he's not interested, so it probably is true.

So if in fact a Ghostbusters 3 happens, you won't be seeing Bill Murray in it along side his original co-stars.