an unknown source gave this info on gb3:
I would have thought by now that it was too late for another sequel to Ghostbusters (1984), but from what I’ve heard about this upcoming movie, it sounds like if it goes ahead it’ll be pretty good. It will be written once again by Harold Ramis and Dan Aykroyd, and will feature many returning cast members from the previous two films, probably the only trilogy of films ever to feature the same actors each time. There will be several differences- the most notable being that this time, there will be no Bill Murray. Well there will, but he will only appear in a brief cameo appearance, and will no longer be a member of the phantom-fighting foursome, as Murray apparently wants nothing to do with the film. It could seem a little different without Murray’s classic ad-libs and humour, but I’m sure that the other cast members will keep the film faithful to its predecessors