A carbon chassis doesn't work.

It removes a lot of weight out of a place you don't want: the lowest place of the car.

So it raises the CoG and will make the car a lot stiffer, two things which are not good in most cases.
The only situation you might want to use a carbon chassis is when you have extreme traction roll. Then you could have a big advantage by using a 4mm thick carbon chassis and a thicker radioplate. But also then you have to take in consideration that the carbon raises the CoG.

Furthermore it changes the heat dissipation around the engine. Some say it will actually improve, so the engine stays cooler, and others say the engine will get hotter. If the engine will run cooler you can try a smaller cooling head on the engine to compensate for the CoG.

@ Lil Bump

Thank you, it was 4 am when i posted my reaction, didn't feel like looking it up in the dictionary.