In my helmet, and every other one, there is a load of hard padding on the other side of the soft cheek pads, right next to my eyes before you get to the casing. Surely a camera lens/microphone combo is able to be inserted there inside this (what I will term) styrofoam, with a wire coming out through the back or side of the helmet underneath all the styrofoam, able to connect to the actual camera hardware, battery and controls that could be the size of an iphone held in a pocket (or in the case of racers, suitably padded within the back-hump of their leathers).
Or the lens could be built into the flexible and removable noseguard/windguard etc.
It shouldn't be too difficult for a quality manufacturer to branch into this niche market