I wanted to make a steam boiler and use it to make electricity, but when the water evaporated, it didn't create any significant amount of pressure. If gasses behaved like BOYL, as in high concentrations of gas created pressure, more realistic things could be made, along with some interesting machines. 

But if this is denied, there is an alternative.

What if when a gas's CTYPE is BOYL, it would have the same behavior as BOYL, along with the behaviors of the original gas? There aren't that many gases, so this wouldn't take much time to implement (I don't really know how the code is structured in TPT, I'm just speculating).