I remember reading about this several years ago. I believe part of the plot was that they have franchised the company, just like in the role playing game. Also, they had new rookie team members. Chris Farley was supposed to be one of them. I forget who the others were. I think Chris Rock was in there too. I honestly would've loved to have seen this movie made.
On a side note, here's a bit of trivia from the IMDB entry of the film: "The original premise of "Ghostbusters" had three main characters: John Belushi, Dan Aykroyd and Eddie Murphy. They fought ghosts in SWAT like suits using wands instead of guns. The ghost named Slimer was known as "Onionhead", and at the end of the movie the Ghostbusters franchise was all over the United States. John Candy also was slated to play Louis. However, with Belushi's death and characters backing out, the script was rewritten and new actors casted."
For more trivia click this link:
http://us.imdb.com/title/tt0087332/trivia