The only things that sit on the bus that talks to the DIS are the radio/TV tuner/Amplifier and telephone module.
There are other bus' in the car used for fearbox, engine, runnin ggear etc, but they connect to other areas of the DIS so shouldn't affect the operation of the car.
The bus used is called the infotainment canbus and is specifically designed for the car ICE installation.
There are modules around which allow you to inject info onto the canbus from your car such as boost, battery etc so I doubt if it would be a problem for a manufacturer to design a canbus interface to the DIS from there radios.
I just don't think that there is a big enough market for it.