Why not have it set in same universe, but present day - so what or how would the world be post GB2
Let's look at 9/11, crazy, tragic event that people could not believe would happen - but it did. Now, right or wrong, it's nothing more than a whisper - an urban myth - conspiracy theory. People argue it was fake, yet life still goes on. People say it was how the media portrayed it, and life goes on. Time does this.
Paranormal events, they all saw what happened, some live with it, others don't.
The GB's themselves disbanded in the 90's after public interest died down - copy cats set up similar bases, paranormal events went wrong - but still happened. But, like 9-11, people move on.
Until now.. a group of scientists stumble across a portal - maybe from the C.E.R.N or HAARP facilities.
Weird goings on get reported and they have to investigate - they research the original GB and track them down - some have moved on, others are willing to help.
A great scene could be Ray opening Egon's old locker, full of notes.
They don the proton packs and get to work.
We have Ghost Busters Extreme