I dunno. I wouldn't argue to put anyone else in charge of this but I'm not sure where they will go with it either. The new cast will surely be taking over.
It might help to move the setting a few years and bump up the ages of the new cast. At least let them age as much as the actors really have aged since 'Afterlife' was filmed. The goofy teenager thing was cute last time but I think the kids should be a notch different next time.
I'm guessing Bill Murray's involvement will be dialed back. The old cast will be mainly Dan & Ernie.
The events of Afterlife are relevant. When Phoebe first called Ray, he almost hung up on her. By the end, he and Winston have definitely had their involvement rekindled. They were always the heart of the team, and I can see then acting in a leadership/advisory role, rather than always being actively out in the field.
I wouldn't discount Peter's or Dana's involvement. The stinger at the end of Afterlife hints that they're not entirely out of the game.
I wouldn't mind seeing Mr. Grooberson stay involved, as a bit of a bridge between the first two films and the new kids. And I want to see more of
said kids. They stepped up hard and, for all the wacky actiony shenanganery, Phoebe and Podcast are solid, and Trevor had a definite arc. Lucky is a good supporting character I want to see more of, as well.
"Firehouse" is slated for release in December of next year. Going by the actors' current ages, I will presume Podcast will be 16, Phoebe will be 17, Trevor will be 20, and Lucky will be 24. So they'll be less "kiddy", and probably have had a bit of an orientation following the cut to end credits in Afterlife.
For me, I still want to see Alyssa Milano as Ivo Shandor's great-granddaughter. And I desperately want a good enough script and relevant reason for him to be there to maybe coax Rick Moranis back as Lewis Tully, the fifth Ghostbuster.