In Quake 2 engine it would still be possible anyway. Plus I didn't say a word about general graphics improvements, probably impossible without engine change.
It's one thing to add polish to the game without drastic changes in engine, therefore in graphics, therefore in requirements. It's another when you ask for improving graphics quality altogether (more detailed polygons, higher res textures, engine able to handle that all). My idea is the former and definitely doable without necessarily changing game engine.
That is an exception, not the rule, as far as CO2 gassing out the front of the barrel.
If it has the backup in basic physics of how it works and can be seen on virtually any pb firing clip AND me and my friends experienced it first hand to nobody's surprise, then it's not what I call exception.