Kuo said 7s will be glass sandwich some how. For S upgrade, it has to be no internal change other than memory and CPU upgrade. It will be too much internal structure redesign to have a mid-frame structure. I don't see how a "open" picture frame like a bumper can avoid bend gate.
My hunch it will be glass laminate over RF transparent metal.
These round of 7S leak might be Android fake (due to USB-C connector).