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.
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