thank you for this great input. We will consider your idea in the future. Please stay in touch with us on our blog and Facebook to see if it might be implemented.
For now, however, we have two options to control volume etc. with touch screens. Please have a look at our instructables:
The 7 inch touch screen from Raspberry Pi: http://www.instructables.com/id/High-End-Sound-with-7-Inch-Touchscreen-Control-Bas/
The 2,8 inch touch screen from watterott: http://www.instructables.com/id/Audio-Solution-with-Control-and-Visualization-on-a/