It seems to me there's room for both in the film. We're talking about Ray and Egon here, you know they haven't been sitting around doing nothing. They're tinkerers. They're going to be constantly coming up with new shit to make their jobs easier. They're going to be improving things, or making things more effective. Does that mean the classic packs can't be in the film? f*** no, but let's be realistic about the reality of the movie universe. There will be new proton packs, and they may or may not look like the classic packs. And there's nothing wrong with that. That's part of what I want to see as a Ghosthead. I want to see all the spiffy new gadgets they've devised to help them bust ghosts. I want to know how they're handling being a franchise. Do they have generic proton packs that they sell to their franchisees? Have they been coming up with newer, heavier duty packs designed to take more abuse? I'd be surprised if all the Ghostbusters have done for the past 20 years is sit on their laurels.
I think there's room in the Ghostbusters universe for more than one style of proton pack. I mean come on, GBII gave us the slime blower, and we all know how divided people are over that thing. Some love it, some hate it. That's always going to happen. The third movie will be no different. You'll have the purists who can't stomach the natural evolution of their beloved GB universe and require everything to remain static/stagnant, and there'll be those who ooh and ahh at the new stuff and get giddy when they see the old stuff too. And then there'll be the people who shrug at the new stuff, don't care for the designs, and just enjoy the movie for what it is.
I personally am hoping for a really wide variety of proton packs. I want to see custom jobs from different franchises. I love the original packs, but most of all I love geeking out over technology, so I'll be excited to see new and different packs as well. Hell, I have a whole sketchbook full of pack designs I've come up with over the years, all based on different ideas about how the technology would evolve, some retaining that home made look, others looking more manufactured and mass produced going along the train of though that GBI has become a multi-billion dollar corporation. They're fun design experiments. I'd hate to deny the production artists of the new movie the fun of finding their own way with the proton packs.
Anyway, that's what I think. And now, just to piss of the purists, here's a doodle I did of an "updated" proton pack