Hi Phil,
I learned from one of Michael Woods interview that he uses his iPad to DJ via an App called Touchable by creating an Adhoc network between The Mac (Ableton) and iPad (Touchable App).
I tried it and it works very well and no concerns around delay or Touch screen. Works very well. I think it will be a great one for you to cover with addition of much more advanced tips on DJing with Ableton and an external Midi since the Djing with ableton 6 video was released.
Adnan Balushi