Die Hard 4=great
Indy 4=pretty good
The 80's revival of hit franchises this decade has a good track record.
Let's see if they can keep it rolling!
Murray as a ghost could work fine. I think Bill has actually put himself, unknowingly?, into always being the face of the franchise. As a ghost he can always return wheras the other GB's will die and be a memory only. Ghost-Venkman could be a "guiding spirit" to future GB's, especially in novel or comic books.
I suggest unknowingly because it seems like he wants a way out of future installments when really he's more cemented now in this capacity I think.