On the first page and we've already got a "make it like Xbox" response.
On topic, I would build a microphone into the controller... But I dunno how that would work with button clicks. There would have to be a pretty good noise rejection algorithm built into it as well. Outside of that, I guess they could make the touchpad a touchscreen? I honestly can't think of much, the DS4 already has a lot going on to consider adding anything else.
I want to see an official PS controller with clear buttons. The X1 looks real cool with 'em.