I hope that there can be some helping with the design of the system and all similar to how the rules were for X.1, partly because this sounds like a good time to ramp and make the Breath weapons neat and effective. Also, Acid Breath doesn't need to be removed I feel, I think a big contributing factor is that most of the other breath weapons are just X free Combat Points with nothing else to show for it. I do agree that Acid Breath needs a huge swing with the Nerfhammer, and it might NEED to be removed regardless.
I feel something like this would be awesome for breath weapons. Obviously things would have to be tweaked a bit.
Breath Weapons: Pick One! And Only One!
Fire Breath (4): +12 Combat. (Not sure what to give this either, but if given something, it should be reduced to +8 Combat)
Lightning Breath (4): +8 Combat and Ranged. When this creature uses it's First Strike ability in the surprise round, it unloads an additional 16 Combat Shockamancy blast in addition to it's normal attack.
Sonic Breath (4): +8 Combat and Siege. When this creature attacks an enemy city with fortifications, it automatically does it's combat to the Walls/Towers/Dungeons of whatever is defending against it in addition to it's normal strike, as if it had the Siege property and deliberately hit the walls.
Acid Breath (4): Target stack defense -1.25 or -1.5 for the rest of the phase.
Smoke Breath (4): Basically what Gust is right now, but only for G classes and competing directly with Acid Breath, rather than having both.
Bubble Breath (4): ??? I'm honestly not sure what to do with this one.
This would obviously need to be refined a bit, but it's the general gist of the ideas I had.