That's an interesting thought. I think there's room for some more utility guns, like the flare, that don't require as much tuning.
A cloud gun: Basically, it shoots a projectile that explodes to create a temporary bit of cloud cover. It doesn't do any damage, so you could make the area fairly big, and it could be useful in a lot of situations. Want to ambush an enemy? Drop a cloud on them, then fire into it with your AoE guns. Need to escape? Shoot a cloud between you and the enemy, then scram while they go around/through it.
Burst rounds would increase the size of the cloud, but maybe shorten the duration. Lesmok would increase distance, Heavy would make it more accurate.
Higher level tactics could even come about, like "They know I like to sneak in through cloud cover, so I'll shoot it over there and then come at them from another direction." It would have a hard counter in the flare gun, but that would require the enemy to "waste" a slot specifically for that.
I think the biggest issue it would cause is hurting sniper builds (I can already hear the chorus of "Great!" that would cause), so you'd need to give it maybe one shot with a long reload time.
