Oh yeah, game-wide events like a ghost uprising or a potential dimensional rift... something where players would NEED to work together would be fantastic. I wouldn't mind there being different pack styles, but as long as one isn't inherently better over another and that all get the same kind of upgrades leaving it an aesthetic choice.
You know, let's hash this out
Let's give this hypothetical game a similar play style as the 09 game where it's mostly 3rd person for the busting segments, but first person for investigations. So, a player will be equipped with your standard gear... a proton pack and a trap with an open equipment slot for a PKE Meter, gigameter, ecto goggles, mood slime spritzer, and really anything else you can think of for secondary gear. After a certain achievement or level/rank/whatever, you gain access to the slimeblower or the experimental pack from the 09 video game (but let's keep it simple and leave it with JUST the slime blower feature, but is less powerful than a full sized slime blower) with their own add-on gear and level up features. Maybe allow a player to open up a second equipment option at the expense of not carrying a trap.
Something to differentiate the PKE from the gigameter could be the PKE has a wider range, but can't pin point the exact location of an entity when you're in a room/building requiring some exploration and investigation. The giga has a smaller range, but can get a pinpoint location on an entity once it's in the scan range as well as reveal any kind of weaknesses it may have (the player would also gain this knowledge after trapping a similar entity once before if they don't have access to a gigameter... think of it sorta like the Pokedex from PokeMon).
The ecto goggles would make invisible entities visible to the player wearing them... but entities would become visible if they're being blasted/slimed allowing for teammates to give assistance easier.
The mood slime spritzer (from the comics) could be used to stun an entity and allow proton streams to be used on it temporarily where normally only a slime blower would be effective.
I mean, there would be nothing to stop a crew going in with just regular packs and brute forcing their way to success except for wanting to clear a case quickly and with as little/much property damage as possible