I am one of those who are fans of the idea of small APS-C mirrorless body.
I found many people are complaining about NEX's giant lens in a thin body, but obviously to achieve the standard flange distance, you have to have either a thin body with a big lens or a thick body. Another option is a collapsible design, while I have seen many people on this board concerning about the building quality of such a collapsible hinge.
Yet another option is to have a completely new lens designed, like what Samsung has done with their NX series. They have made new pancakes with shorter flange distance. But this also comes with two problems: 1. The old lenses of pentax are no longer usable, which is one of the major reasons many people still stay with Pentax. 2. The edge IQ could be a concern because the angle of the incoming light will have to be much smaller to really reduce the thick.
I am not sure if anyone has discussed about this idea before. This is my design: A new mirror was added to reflect all the light from the lens to the sensor. The body in theory can be made as thin as the height of the sensor, which is 15.7mm for a APS-C sensor, or 24mm for a full-frame sensor! (The current dslr design allows minimal body thickness to be 45.46 mm for pentax). If my design is really achievable, then with a pancake installed we can really put this camera into our jeans pocket.
I think the major concern will be the quality of the mirror. It must be of very high quality. No distortion, very limited absorption of light. I don't know much about the engineering of mirrors, but as mirror lens could be made in very cheap price, my guess is a mirror camera is also doable.
Let me know your thoughts