I've tested out touch screen once, at a time when Sonar was just one revision short of supporting it, on Windows 7, not the ideal touch screen platform. I was thinking the OS would translate touches to mouse events, and I was doing only one test - to mix a song using touch screen. But that didn't work well with Sonar at that time, so I was actually testing it with Reaper. The fader size is similar to Sonar, and Reaper works well responding to touches.
However, my conclusion that touch screen is not for me due to the fader being too small to make fine adjustment on my 21" Dell. It may be better on a 27" or larger screen, but that means you have to spread your arms out. If you mock up a touch screen practical for your use, you'll imagine how close the monitor needs to be placed in front of you.
I think Sonar's fader needs to have feature to be re sized in order to mix with touch screen. Not completely rule it out yet, I'm still thinking touch screen may work well for step sequencer drums programming. As I'm still on Windows 7, and I can't touch-hold to delete a step sequencer note, but folks here responded that this is possible, presumably on Windows 8 or greater.