Reduced visibility is the most cancerous thing you can have in a game where you can already see only 7 tiles in each direction. Especially since every pouncer can pounce from 5th tile. No matter how good you would make gasmaks, just the visibility alone is a nail in the coffin for that.
Also you think about too big cooperation for random SS13 players. No player (both marine and beno) will connect in hivemind to do such a stunt. Maybe in ARMA, or game like that you could have stuff of this caliber.
If gasmask has ever to return, it should slow you down only. Not only it would bring a bit of realism, since you can't really run far and fast with gasmask as you can't get enough oxygen with each breathing cycle (unless its some fancy gasmask with airpump). Even then running into gas is a death sentence for marines, since gas already reduces their vision too and benos can see them trough. Especially now when 3 beno castes have acid spray and one can neurospam.
Yes, C-acronym can be broken, but its not fun to do that, its tedious, its based on luck and it will always bring a lot of casualities. All of that to push benos to next chokepoint. And looking at every map... Every map has caves and every cave has multiple chokepoints.
Marine tactics to turtle and beno tactics to murderball are things that players naturally fall into. If you are afraid of you character death, you run when you see multiple enemies. If you are not afraid of your character death, you rush the enemy, no matter what. As simple as that.
In the past of boomer politics, it was easy to be afraid of your IC life as marine, since odds were always against you, so standard player usually turtled in that moment. Benos then were always at adventage, so they didn't had to worry about their IC life since they could always quickly retreat to reheal fast and easy in less than a minute. Now its more, or less balanced, so tactics are flexible. This is where robustos take their part. They lead by example. If you sit behind a cade, waiting for your death, but then you see few confident mariens who despite all odds go past the cades and rush, you start to feel that this might be it and you go with them, causing domino murderball.