I think the problem is they've engineered themselves into a bit of a dead end. The whole idea behind the design is the internals sit in the camera 'plateau' and then it's just screen and battery in the rest of the device, but introduce a second camera and then the space you've got rapidly shrinks. So you'd need a larger plateau, but then it's getting to the point where this isn't a thin device any more. And of course a second speaker can't sit in the plateau.
Maybe it's just a bad idea.
Nothing wrong with miniaturising components but maybe they don't need to sit in a plateau.