Then you can only adjust one thing at a time—so you’ve just created the worst of both worlds with a multi-touch display and live music software.
There is a reason people serious about doing music keep using physical knobs to change values in their software. I’m entirely convinced the sole reason DAWs use virtual knobs despite them being such a poor UX element is because people will map them to MIDI knobs anyway and that keeps the software and physical world looking the same.
I do it all the time on an iPad. It handles up to 5 simultaneous controls very well.
Prompting the obvious question: Why eleven?
At that point I guess the physical resemblance is a virtue.