I'm still kind of dumbfounded that the 7 Plus has two cameras side-by-side and apparently ISN'T using them to capture 3D images. One would think this would be the best/most obvious application.
You can still do it, you just have to tweak your calibration parameters to accept a different focal length for the second camera. It's a huge pain but doable.
They're too close together for that. Your eyes are about 6cm (~2.4in) apart, those lenses look like they're 1cm apart. You need enough distance between them to capture stereoscopic images.
Remember Touch ID hardware > Apple Pay? I expect we'll see something similar with the dual cameras.
I expect either VR support, 3D imaging, or using them+dynamic light sensing of iPad Pro to have a "reactive" UI where gradients in the UI behave as if they might have real world lighting applied to them