I love the thought of companies trying to re-invent the way we play games (Wiipad, Rift, IR, hopefully Kinect 2.0), though I can't really say I'm feeling the idea of a touchpad at the moment.
I have my dualshock in hand and swiping the middle of the controller doesn't see too intuitive with the current placement of the analog sticks. I'd assume that has to be changed to make it more feasible, as some mockups have already shown.
The best thing about it, as already mentioned, is giving the user an added method of input. For example, in an FPS, maybe swipe left/right to switch weapons, swipe up to use a grenade, swipe down to do a 180 turn, two finger swipe down to bring up a menu. It can be very useful in this regard, since we wouldn't need shitty button combinations anymore to do trivial actions in control heavy games.
From a technical point of view, it can still use bluetooth as its wireless protocol considering it's not doing any heavy video streaming like the WiiU, so the added costs should be minimal in comparison.